Move FilePathWatcher to base/files.

FilePathWatcher is going to be used in future for monitoring
changes to /etc/resolv.conf so it needs live somewhere where
various consumers can get at it without incurring the wrath
of the layering gods.

TEST=existing tests
BUG=67734

Review URL: http://codereview.chromium.org/6793020

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@81606 0039d316-1c4b-4281-b951-d872f2087c98

8 files changed, 2053 insertions, 0 deletions

diff --git a/base/files/OWNERS b/base/files/OWNERS
new file mode 100644
index 0000000..ef0b156
--- /dev/null
+++ b/base/files/OWNERS
@@ -0,0 +1,3 @@
+# for file_path_watcher*
+mnissler@chromium.org
+dmaclach@chromium.org
diff --git a/base/files/file_path_watcher.cc b/base/files/file_path_watcher.cc
new file mode 100644
index 0000000..7ce64ac
--- /dev/null
+++ b/base/files/file_path_watcher.cc
@@ -0,0 +1,33 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Cross platform methods for FilePathWatcher. See the various platform
+// specific implementation files, too.
+
+#include "base/files/file_path_watcher.h"
+
+#include "base/logging.h"
+#include "base/message_loop.h"
+
+namespace base {
+namespace files {
+
+FilePathWatcher::~FilePathWatcher() {
+  impl_->Cancel();
+}
+
+bool FilePathWatcher::Watch(const FilePath& path, Delegate* delegate) {
+  DCHECK(path.IsAbsolute());
+  return impl_->Watch(path, delegate);
+}
+
+FilePathWatcher::PlatformDelegate::PlatformDelegate(): cancelled_(false) {
+}
+
+FilePathWatcher::PlatformDelegate::~PlatformDelegate() {
+  DCHECK(is_cancelled());
+}
+
+}  // namespace files
+}  // namespace base
diff --git a/base/files/file_path_watcher.h b/base/files/file_path_watcher.h
new file mode 100644
index 0000000..2cf95c6
--- /dev/null
+++ b/base/files/file_path_watcher.h
@@ -0,0 +1,128 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This module provides a way to monitor a file or directory for changes.
+
+#ifndef BASE_FILES_FILE_PATH_WATCHER_H_
+#define BASE_FILES_FILE_PATH_WATCHER_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/file_path.h"
+#include "base/memory/ref_counted.h"
+#include "base/message_loop_proxy.h"
+
+namespace base {
+namespace files {
+
+// This class lets you register interest in changes on a FilePath.
+// The delegate will get called whenever the file or directory referenced by the
+// FilePath is changed, including created or deleted. Due to limitations in the
+// underlying OS APIs, FilePathWatcher has slightly different semantics on OS X
+// than on Windows or Linux. FilePathWatcher on Linux and Windows will detect
+// modifications to files in a watched directory. FilePathWatcher on Mac will
+// detect the creation and deletion of files in a watched directory, but will
+// not detect modifications to those files. See file_path_watcher_mac.cc for
+// details.
+class FilePathWatcher {
+ public:
+  // Declares the callback client code implements to receive notifications. Note
+  // that implementations of this interface should not keep a reference to the
+  // corresponding FileWatcher object to prevent a reference cycle.
+  class Delegate : public base::RefCountedThreadSafe<Delegate> {
+   public:
+    virtual ~Delegate() {}
+    virtual void OnFilePathChanged(const FilePath& path) = 0;
+    // Called when platform specific code detected an error. The watcher will
+    // not call OnFilePathChanged for future changes.
+    virtual void OnFilePathError(const FilePath& path) {}
+  };
+
+  FilePathWatcher();
+  ~FilePathWatcher();
+
+  // Register interest in any changes on |path|. OnPathChanged will be called
+  // back for each change. Returns true on success.
+  // OnFilePathChanged() will be called on the same thread as Watch() is called,
+  // which should have a MessageLoop of TYPE_IO.
+  bool Watch(const FilePath& path, Delegate* delegate) WARN_UNUSED_RESULT;
+
+  class PlatformDelegate;
+
+  // A custom Task that always cleans up the PlatformDelegate, either when
+  // executed or when deleted without having been executed at all, as can
+  // happen during shutdown.
+  class CancelTask : public Task {
+   public:
+    CancelTask(PlatformDelegate* delegate): delegate_(delegate) {}
+    virtual ~CancelTask() {
+      delegate_->CancelOnMessageLoopThread();
+    }
+
+    virtual void Run() {
+      delegate_->CancelOnMessageLoopThread();
+    }
+   private:
+    scoped_refptr<PlatformDelegate> delegate_;
+
+    DISALLOW_COPY_AND_ASSIGN(CancelTask);
+  };
+
+  // Used internally to encapsulate different members on different platforms.
+  class PlatformDelegate : public base::RefCountedThreadSafe<PlatformDelegate> {
+   public:
+    PlatformDelegate();
+
+    // Start watching for the given |path| and notify |delegate| about changes.
+    virtual bool Watch(const FilePath& path,
+                       Delegate* delegate) WARN_UNUSED_RESULT = 0;
+
+    // Stop watching. This is called from FilePathWatcher's dtor in order to
+    // allow to shut down properly while the object is still alive.
+    // It can be called from any thread.
+    virtual void Cancel() = 0;
+
+   protected:
+    virtual ~PlatformDelegate();
+
+    // Stop watching. This is only called on the thread of the appropriate
+    // message loop. Since it can also be called more than once, it should
+    // check |is_cancelled()| to avoid duplicate work.
+    virtual void CancelOnMessageLoopThread() = 0;
+
+    scoped_refptr<base::MessageLoopProxy> message_loop() const {
+      return message_loop_;
+    }
+
+    void set_message_loop(base::MessageLoopProxy* loop) {
+      message_loop_ = loop;
+    }
+
+    // Must be called before the PlatformDelegate is deleted.
+    void set_cancelled() {
+      cancelled_ = true;
+    }
+
+    bool is_cancelled() const {
+      return cancelled_;
+    }
+
+   private:
+    friend class base::RefCountedThreadSafe<PlatformDelegate>;
+    friend class CancelTask;
+
+    scoped_refptr<base::MessageLoopProxy> message_loop_;
+    bool cancelled_;
+  };
+
+ private:
+  scoped_refptr<PlatformDelegate> impl_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilePathWatcher);
+};
+
+}  // namespace files
+}  // namespace base
+
+#endif  // BASE_FILES_FILE_PATH_WATCHER_H_
diff --git a/base/files/file_path_watcher_browsertest.cc b/base/files/file_path_watcher_browsertest.cc
new file mode 100644
index 0000000..d623c90
--- /dev/null
+++ b/base/files/file_path_watcher_browsertest.cc
@@ -0,0 +1,622 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/files/file_path_watcher.h"
+
+#include <set>
+
+#if defined(OS_WIN)
+#include <windows.h>
+#include <aclapi.h>
+#elif defined(OS_POSIX)
+#include <sys/stat.h>
+#endif
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/file_path.h"
+#include "base/file_util.h"
+#include "base/memory/scoped_temp_dir.h"
+#include "base/message_loop.h"
+#include "base/message_loop_proxy.h"
+#include "base/path_service.h"
+#include "base/string_util.h"
+#include "base/stl_util-inl.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/test/test_timeouts.h"
+#include "base/threading/thread.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+namespace files {
+
+namespace {
+
+class TestDelegate;
+
+// Aggregates notifications from the test delegates and breaks the message loop
+// the test thread is waiting on once they all came in.
+class NotificationCollector
+    : public base::RefCountedThreadSafe<NotificationCollector> {
+ public:
+  NotificationCollector()
+      : loop_(base::MessageLoopProxy::CreateForCurrentThread()) {}
+
+  // Called from the file thread by the delegates.
+  void OnChange(TestDelegate* delegate) {
+    loop_->PostTask(FROM_HERE,
+                    NewRunnableMethod(this,
+                                      &NotificationCollector::RecordChange,
+                                      make_scoped_refptr(delegate)));
+  }
+
+  void Register(TestDelegate* delegate) {
+    delegates_.insert(delegate);
+  }
+
+  void Reset() {
+    signaled_.clear();
+  }
+
+  bool Success() {
+    return signaled_ == delegates_;
+  }
+
+ private:
+  void RecordChange(TestDelegate* delegate) {
+    ASSERT_TRUE(loop_->BelongsToCurrentThread());
+    ASSERT_TRUE(delegates_.count(delegate));
+    signaled_.insert(delegate);
+
+    // Check whether all delegates have been signaled.
+    if (signaled_ == delegates_)
+      loop_->PostTask(FROM_HERE, new MessageLoop::QuitTask());
+  }
+
+  // Set of registered delegates.
+  std::set<TestDelegate*> delegates_;
+
+  // Set of signaled delegates.
+  std::set<TestDelegate*> signaled_;
+
+  // The loop we should break after all delegates signaled.
+  scoped_refptr<base::MessageLoopProxy> loop_;
+};
+
+// A mock FilePathWatcher::Delegate for testing. I'd rather use gmock, but it's
+// not thread safe for setting expectations, so the test code couldn't safely
+// reset expectations while the file watcher is running. In order to allow this,
+// we keep simple thread safe status flags in TestDelegate.
+class TestDelegate : public FilePathWatcher::Delegate {
+ public:
+  // The message loop specified by |loop| will be quit if a notification is
+  // received while the delegate is |armed_|. Note that the testing code must
+  // guarantee |loop| outlives the file thread on which OnFilePathChanged runs.
+  explicit TestDelegate(NotificationCollector* collector)
+      : collector_(collector) {
+    collector_->Register(this);
+  }
+
+  virtual void OnFilePathChanged(const FilePath&) {
+    collector_->OnChange(this);
+  }
+
+  virtual void OnFilePathError(const FilePath& path) {
+    ADD_FAILURE() << "Error " << path.value();
+  }
+
+ private:
+  scoped_refptr<NotificationCollector> collector_;
+
+  DISALLOW_COPY_AND_ASSIGN(TestDelegate);
+};
+
+// A helper class for setting up watches on the file thread.
+class SetupWatchTask : public Task {
+ public:
+  SetupWatchTask(const FilePath& target,
+                 FilePathWatcher* watcher,
+                 FilePathWatcher::Delegate* delegate,
+                 bool* result,
+                 base::WaitableEvent* completion)
+      : target_(target),
+        watcher_(watcher),
+        delegate_(delegate),
+        result_(result),
+        completion_(completion) {}
+
+  void Run() {
+    *result_ = watcher_->Watch(target_, delegate_);
+    completion_->Signal();
+  }
+
+ private:
+  const FilePath target_;
+  FilePathWatcher* watcher_;
+  FilePathWatcher::Delegate* delegate_;
+  bool* result_;
+  base::WaitableEvent* completion_;
+
+  DISALLOW_COPY_AND_ASSIGN(SetupWatchTask);
+};
+
+class FilePathWatcherTest : public testing::Test {
+ public:
+  FilePathWatcherTest()
+      : file_thread_("FilePathWatcherTest") {}
+
+  virtual ~FilePathWatcherTest() {}
+
+ protected:
+  virtual void SetUp() {
+    // Create a separate file thread in order to test proper thread usage.
+    base::Thread::Options options(MessageLoop::TYPE_IO, 0);
+    ASSERT_TRUE(file_thread_.StartWithOptions(options));
+    ASSERT_TRUE(temp_dir_.CreateUniqueTempDir());
+    collector_ = new NotificationCollector();
+  }
+
+  virtual void TearDown() {
+    loop_.RunAllPending();
+  }
+
+  FilePath test_file() {
+    return temp_dir_.path().AppendASCII("FilePathWatcherTest");
+  }
+
+  // Write |content| to |file|. Returns true on success.
+  bool WriteFile(const FilePath& file, const std::string& content) {
+    int write_size = file_util::WriteFile(file, content.c_str(),
+                                          content.length());
+    return write_size == static_cast<int>(content.length());
+  }
+
+  bool SetupWatch(const FilePath& target,
+                  FilePathWatcher* watcher,
+                  FilePathWatcher::Delegate* delegate) WARN_UNUSED_RESULT {
+    base::WaitableEvent completion(false, false);
+    bool result;
+    file_thread_.message_loop_proxy()->PostTask(FROM_HERE,
+         new SetupWatchTask(target,
+                            watcher,
+                            delegate,
+                            &result,
+                            &completion));
+    completion.Wait();
+    return result;
+  }
+
+  bool WaitForEvents() WARN_UNUSED_RESULT {
+    collector_->Reset();
+    loop_.Run();
+    return collector_->Success();
+  }
+
+  NotificationCollector* collector() { return collector_.get(); }
+
+  MessageLoop loop_;
+  base::Thread file_thread_;
+  ScopedTempDir temp_dir_;
+  scoped_refptr<NotificationCollector> collector_;
+};
+
+// Basic test: Create the file and verify that we notice.
+TEST_F(FilePathWatcherTest, NewFile) {
+  FilePathWatcher watcher;
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(test_file(), &watcher, delegate.get()));
+
+  ASSERT_TRUE(WriteFile(test_file(), "content"));
+  ASSERT_TRUE(WaitForEvents());
+}
+
+// Verify that modifying the file is caught.
+TEST_F(FilePathWatcherTest, ModifiedFile) {
+  ASSERT_TRUE(WriteFile(test_file(), "content"));
+
+  FilePathWatcher watcher;
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(test_file(), &watcher, delegate.get()));
+
+  // Now make sure we get notified if the file is modified.
+  ASSERT_TRUE(WriteFile(test_file(), "new content"));
+  ASSERT_TRUE(WaitForEvents());
+}
+
+// Verify that moving the file into place is caught.
+TEST_F(FilePathWatcherTest, MovedFile) {
+  FilePath source_file(temp_dir_.path().AppendASCII("source"));
+  ASSERT_TRUE(WriteFile(source_file, "content"));
+
+  FilePathWatcher watcher;
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(test_file(), &watcher, delegate.get()));
+
+  // Now make sure we get notified if the file is modified.
+  ASSERT_TRUE(file_util::Move(source_file, test_file()));
+  ASSERT_TRUE(WaitForEvents());
+}
+
+TEST_F(FilePathWatcherTest, DeletedFile) {
+  ASSERT_TRUE(WriteFile(test_file(), "content"));
+
+  FilePathWatcher watcher;
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(test_file(), &watcher, delegate.get()));
+
+  // Now make sure we get notified if the file is deleted.
+  file_util::Delete(test_file(), false);
+  ASSERT_TRUE(WaitForEvents());
+}
+
+// Used by the DeleteDuringNotify test below.
+// Deletes the FilePathWatcher when it's notified.
+class Deleter : public FilePathWatcher::Delegate {
+ public:
+  Deleter(FilePathWatcher* watcher, MessageLoop* loop)
+      : watcher_(watcher),
+        loop_(loop) {
+  }
+
+  virtual void OnFilePathChanged(const FilePath& path) {
+    watcher_.reset();
+    loop_->PostTask(FROM_HERE, new MessageLoop::QuitTask());
+  }
+
+  scoped_ptr<FilePathWatcher> watcher_;
+  MessageLoop* loop_;
+};
+
+// Verify that deleting a watcher during the callback doesn't crash.
+TEST_F(FilePathWatcherTest, DeleteDuringNotify) {
+  FilePathWatcher* watcher = new FilePathWatcher;
+  // Takes ownership of watcher.
+  scoped_refptr<Deleter> deleter(new Deleter(watcher, &loop_));
+  ASSERT_TRUE(SetupWatch(test_file(), watcher, deleter.get()));
+
+  ASSERT_TRUE(WriteFile(test_file(), "content"));
+  ASSERT_TRUE(WaitForEvents());
+
+  // We win if we haven't crashed yet.
+  // Might as well double-check it got deleted, too.
+  ASSERT_TRUE(deleter->watcher_.get() == NULL);
+}
+
+// Verify that deleting the watcher works even if there is a pending
+// notification.
+TEST_F(FilePathWatcherTest, DestroyWithPendingNotification) {
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  FilePathWatcher* watcher = new FilePathWatcher;
+  ASSERT_TRUE(SetupWatch(test_file(), watcher, delegate.get()));
+  ASSERT_TRUE(WriteFile(test_file(), "content"));
+  file_thread_.message_loop_proxy()->DeleteSoon(FROM_HERE, watcher);
+}
+
+TEST_F(FilePathWatcherTest, MultipleWatchersSingleFile) {
+  FilePathWatcher watcher1, watcher2;
+  scoped_refptr<TestDelegate> delegate1(new TestDelegate(collector()));
+  scoped_refptr<TestDelegate> delegate2(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(test_file(), &watcher1, delegate1.get()));
+  ASSERT_TRUE(SetupWatch(test_file(), &watcher2, delegate2.get()));
+
+  ASSERT_TRUE(WriteFile(test_file(), "content"));
+  ASSERT_TRUE(WaitForEvents());
+}
+
+// Verify that watching a file whose parent directory doesn't exist yet works if
+// the directory and file are created eventually.
+TEST_F(FilePathWatcherTest, NonExistentDirectory) {
+  FilePathWatcher watcher;
+  FilePath dir(temp_dir_.path().AppendASCII("dir"));
+  FilePath file(dir.AppendASCII("file"));
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(file, &watcher, delegate.get()));
+
+  ASSERT_TRUE(file_util::CreateDirectory(dir));
+
+  ASSERT_TRUE(WriteFile(file, "content"));
+
+  VLOG(1) << "Waiting for file creation";
+  ASSERT_TRUE(WaitForEvents());
+
+  ASSERT_TRUE(WriteFile(file, "content v2"));
+  VLOG(1) << "Waiting for file change";
+  ASSERT_TRUE(WaitForEvents());
+
+  ASSERT_TRUE(file_util::Delete(file, false));
+  VLOG(1) << "Waiting for file deletion";
+  ASSERT_TRUE(WaitForEvents());
+}
+
+// Exercises watch reconfiguration for the case that directories on the path
+// are rapidly created.
+TEST_F(FilePathWatcherTest, DirectoryChain) {
+  FilePath path(temp_dir_.path());
+  std::vector<std::string> dir_names;
+  for (int i = 0; i < 20; i++) {
+    std::string dir(StringPrintf("d%d", i));
+    dir_names.push_back(dir);
+    path = path.AppendASCII(dir);
+  }
+
+  FilePathWatcher watcher;
+  FilePath file(path.AppendASCII("file"));
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(file, &watcher, delegate.get()));
+
+  FilePath sub_path(temp_dir_.path());
+  for (std::vector<std::string>::const_iterator d(dir_names.begin());
+       d != dir_names.end(); ++d) {
+    sub_path = sub_path.AppendASCII(*d);
+    ASSERT_TRUE(file_util::CreateDirectory(sub_path));
+  }
+  VLOG(1) << "Create File";
+  ASSERT_TRUE(WriteFile(file, "content"));
+  VLOG(1) << "Waiting for file creation";
+  ASSERT_TRUE(WaitForEvents());
+
+  ASSERT_TRUE(WriteFile(file, "content v2"));
+  VLOG(1) << "Waiting for file modification";
+  ASSERT_TRUE(WaitForEvents());
+}
+
+TEST_F(FilePathWatcherTest, DisappearingDirectory) {
+  FilePathWatcher watcher;
+  FilePath dir(temp_dir_.path().AppendASCII("dir"));
+  FilePath file(dir.AppendASCII("file"));
+  ASSERT_TRUE(file_util::CreateDirectory(dir));
+  ASSERT_TRUE(WriteFile(file, "content"));
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(file, &watcher, delegate.get()));
+
+  ASSERT_TRUE(file_util::Delete(dir, true));
+  ASSERT_TRUE(WaitForEvents());
+}
+
+// Tests that a file that is deleted and reappears is tracked correctly.
+TEST_F(FilePathWatcherTest, DeleteAndRecreate) {
+  ASSERT_TRUE(WriteFile(test_file(), "content"));
+  FilePathWatcher watcher;
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(test_file(), &watcher, delegate.get()));
+
+  ASSERT_TRUE(file_util::Delete(test_file(), false));
+  VLOG(1) << "Waiting for file deletion";
+  ASSERT_TRUE(WaitForEvents());
+
+  ASSERT_TRUE(WriteFile(test_file(), "content"));
+  VLOG(1) << "Waiting for file creation";
+  ASSERT_TRUE(WaitForEvents());
+}
+
+TEST_F(FilePathWatcherTest, WatchDirectory) {
+  FilePathWatcher watcher;
+  FilePath dir(temp_dir_.path().AppendASCII("dir"));
+  FilePath file1(dir.AppendASCII("file1"));
+  FilePath file2(dir.AppendASCII("file2"));
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(dir, &watcher, delegate.get()));
+
+  ASSERT_TRUE(file_util::CreateDirectory(dir));
+  VLOG(1) << "Waiting for directory creation";
+  ASSERT_TRUE(WaitForEvents());
+
+  ASSERT_TRUE(WriteFile(file1, "content"));
+  VLOG(1) << "Waiting for file1 creation";
+  ASSERT_TRUE(WaitForEvents());
+
+#if !defined(OS_MACOSX)
+  // Mac implementation does not detect files modified in a directory.
+  ASSERT_TRUE(WriteFile(file1, "content v2"));
+  VLOG(1) << "Waiting for file1 modification";
+  ASSERT_TRUE(WaitForEvents());
+#endif  // !OS_MACOSX
+
+  ASSERT_TRUE(file_util::Delete(file1, false));
+  VLOG(1) << "Waiting for file1 deletion";
+  ASSERT_TRUE(WaitForEvents());
+
+  ASSERT_TRUE(WriteFile(file2, "content"));
+  VLOG(1) << "Waiting for file2 creation";
+  ASSERT_TRUE(WaitForEvents());
+}
+
+TEST_F(FilePathWatcherTest, MoveParent) {
+  FilePathWatcher file_watcher;
+  FilePathWatcher subdir_watcher;
+  FilePath dir(temp_dir_.path().AppendASCII("dir"));
+  FilePath dest(temp_dir_.path().AppendASCII("dest"));
+  FilePath subdir(dir.AppendASCII("subdir"));
+  FilePath file(subdir.AppendASCII("file"));
+  scoped_refptr<TestDelegate> file_delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(file, &file_watcher, file_delegate.get()));
+  scoped_refptr<TestDelegate> subdir_delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(subdir, &subdir_watcher, subdir_delegate.get()));
+
+  // Setup a directory hierarchy.
+  ASSERT_TRUE(file_util::CreateDirectory(subdir));
+  ASSERT_TRUE(WriteFile(file, "content"));
+  VLOG(1) << "Waiting for file creation";
+  ASSERT_TRUE(WaitForEvents());
+
+  // Move the parent directory.
+  file_util::Move(dir, dest);
+  VLOG(1) << "Waiting for directory move";
+  ASSERT_TRUE(WaitForEvents());
+}
+
+TEST_F(FilePathWatcherTest, MoveChild) {
+  FilePathWatcher file_watcher;
+  FilePathWatcher subdir_watcher;
+  FilePath source_dir(temp_dir_.path().AppendASCII("source"));
+  FilePath source_subdir(source_dir.AppendASCII("subdir"));
+  FilePath source_file(source_subdir.AppendASCII("file"));
+  FilePath dest_dir(temp_dir_.path().AppendASCII("dest"));
+  FilePath dest_subdir(dest_dir.AppendASCII("subdir"));
+  FilePath dest_file(dest_subdir.AppendASCII("file"));
+
+  // Setup a directory hierarchy.
+  ASSERT_TRUE(file_util::CreateDirectory(source_subdir));
+  ASSERT_TRUE(WriteFile(source_file, "content"));
+
+  scoped_refptr<TestDelegate> file_delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(dest_file, &file_watcher, file_delegate.get()));
+  scoped_refptr<TestDelegate> subdir_delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(dest_subdir, &subdir_watcher, subdir_delegate.get()));
+
+  // Move the directory into place, s.t. the watched file appears.
+  ASSERT_TRUE(file_util::Move(source_dir, dest_dir));
+  ASSERT_TRUE(WaitForEvents());
+}
+
+#if !defined(OS_LINUX)
+// Linux implementation of FilePathWatcher doesn't catch attribute changes.
+// http://crbug.com/78043
+
+// Verify that changing attributes on a file is caught
+TEST_F(FilePathWatcherTest, FileAttributesChanged) {
+  ASSERT_TRUE(WriteFile(test_file(), "content"));
+  FilePathWatcher watcher;
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(test_file(), &watcher, delegate.get()));
+
+  // Now make sure we get notified if the file is modified.
+  ASSERT_TRUE(file_util::MakeFileUnreadable(test_file()));
+  ASSERT_TRUE(WaitForEvents());
+}
+
+#endif  // !OS_LINUX
+
+enum Permission {
+  Read,
+  Write,
+  Execute
+};
+
+bool ChangeFilePermissions(const FilePath& path, Permission perm, bool allow) {
+#if defined(OS_POSIX)
+  struct stat stat_buf;
+
+  if (stat(path.value().c_str(), &stat_buf) != 0)
+    return false;
+
+  mode_t mode = 0;
+  switch (perm) {
+    case Read:
+      mode = S_IRUSR | S_IRGRP | S_IROTH;
+      break;
+    case Write:
+      mode = S_IWUSR | S_IWGRP | S_IWOTH;
+      break;
+    case Execute:
+      mode = S_IXUSR | S_IXGRP | S_IXOTH;
+      break;
+    default:
+      ADD_FAILURE() << "unknown perm " << perm;
+      return false;
+  }
+  if (allow) {
+    stat_buf.st_mode |= mode;
+  } else {
+    stat_buf.st_mode &= ~mode;
+  }
+  return chmod(path.value().c_str(), stat_buf.st_mode) == 0;
+
+#elif defined(OS_WIN)
+  PACL old_dacl;
+  PSECURITY_DESCRIPTOR security_descriptor;
+  if (GetNamedSecurityInfo(const_cast<wchar_t*>(path.value().c_str()),
+                           SE_FILE_OBJECT,
+                           DACL_SECURITY_INFORMATION, NULL, NULL, &old_dacl,
+                           NULL, &security_descriptor) != ERROR_SUCCESS)
+    return false;
+
+  DWORD mode = 0;
+  switch (perm) {
+    case Read:
+      mode = GENERIC_READ;
+      break;
+    case Write:
+      mode = GENERIC_WRITE;
+      break;
+    case Execute:
+      mode = GENERIC_EXECUTE;
+      break;
+    default:
+      ADD_FAILURE() << "unknown perm " << perm;
+      return false;
+  }
+
+  // Deny Read access for the current user.
+  EXPLICIT_ACCESS change;
+  change.grfAccessPermissions = mode;
+  change.grfAccessMode = allow ? GRANT_ACCESS : DENY_ACCESS;
+  change.grfInheritance = 0;
+  change.Trustee.pMultipleTrustee = NULL;
+  change.Trustee.MultipleTrusteeOperation = NO_MULTIPLE_TRUSTEE;
+  change.Trustee.TrusteeForm = TRUSTEE_IS_NAME;
+  change.Trustee.TrusteeType = TRUSTEE_IS_USER;
+  change.Trustee.ptstrName = L"CURRENT_USER";
+
+  PACL new_dacl;
+  if (SetEntriesInAcl(1, &change, old_dacl, &new_dacl) != ERROR_SUCCESS) {
+    LocalFree(security_descriptor);
+    return false;
+  }
+
+  DWORD rc = SetNamedSecurityInfo(const_cast<wchar_t*>(path.value().c_str()),
+                                  SE_FILE_OBJECT, DACL_SECURITY_INFORMATION,
+                                  NULL, NULL, new_dacl, NULL);
+  LocalFree(security_descriptor);
+  LocalFree(new_dacl);
+
+  return rc == ERROR_SUCCESS;
+#else
+  NOTIMPLEMENTED();
+  return false;
+#endif
+}
+
+#if defined(OS_MACOSX)
+// Linux implementation of FilePathWatcher doesn't catch attribute changes.
+// http://crbug.com/78043
+// Windows implementation of FilePathWatcher catches attribute changes that
+// don't affect the path being watched.
+// http://crbug.com/78045
+
+// Verify that changing attributes on a directory works.
+TEST_F(FilePathWatcherTest, DirAttributesChanged) {
+  FilePath test_dir1(temp_dir_.path().AppendASCII("DirAttributesChangedDir1"));
+  FilePath test_dir2(test_dir1.AppendASCII("DirAttributesChangedDir2"));
+  FilePath test_file(test_dir2.AppendASCII("DirAttributesChangedFile"));
+  // Setup a directory hierarchy.
+  ASSERT_TRUE(file_util::CreateDirectory(test_dir1));
+  ASSERT_TRUE(file_util::CreateDirectory(test_dir2));
+  ASSERT_TRUE(WriteFile(test_file, "content"));
+
+  FilePathWatcher watcher;
+  scoped_refptr<TestDelegate> delegate(new TestDelegate(collector()));
+  ASSERT_TRUE(SetupWatch(test_file, &watcher, delegate.get()));
+
+  // We should not get notified in this case as it hasn't affected our ability
+  // to access the file.
+  ASSERT_TRUE(ChangeFilePermissions(test_dir1, Read, false));
+  loop_.PostDelayedTask(FROM_HERE,
+                        new MessageLoop::QuitTask,
+                        TestTimeouts::tiny_timeout_ms());
+  ASSERT_FALSE(WaitForEvents());
+  ASSERT_TRUE(ChangeFilePermissions(test_dir1, Read, true));
+
+  // We should get notified in this case because filepathwatcher can no
+  // longer access the file
+  ASSERT_TRUE(ChangeFilePermissions(test_dir1, Execute, false));
+  ASSERT_TRUE(WaitForEvents());
+  ASSERT_TRUE(ChangeFilePermissions(test_dir1, Execute, true));
+}
+
+#endif  // OS_MACOSX
+}  // namespace
+
+}  // namespace files
+}  // namespace base
diff --git a/base/files/file_path_watcher_linux.cc b/base/files/file_path_watcher_linux.cc
new file mode 100644
index 0000000..0fb10e4
--- /dev/null
+++ b/base/files/file_path_watcher_linux.cc
@@ -0,0 +1,462 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/files/file_path_watcher.h"
+
+#include <errno.h>
+#include <string.h>
+#include <sys/inotify.h>
+#include <sys/ioctl.h>
+#include <sys/select.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <set>
+#include <utility>
+#include <vector>
+
+#include "base/eintr_wrapper.h"
+#include "base/file_path.h"
+#include "base/file_util.h"
+#include "base/hash_tables.h"
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/message_loop.h"
+#include "base/message_loop_proxy.h"
+#include "base/synchronization/lock.h"
+#include "base/task.h"
+#include "base/threading/thread.h"
+
+namespace base {
+namespace files {
+
+namespace {
+
+class FilePathWatcherImpl;
+
+// Singleton to manage all inotify watches.
+// TODO(tony): It would be nice if this wasn't a singleton.
+// http://crbug.com/38174
+class InotifyReader {
+ public:
+  typedef int Watch;  // Watch descriptor used by AddWatch and RemoveWatch.
+  static const Watch kInvalidWatch = -1;
+
+  // Watch directory |path| for changes. |watcher| will be notified on each
+  // change. Returns kInvalidWatch on failure.
+  Watch AddWatch(const FilePath& path, FilePathWatcherImpl* watcher);
+
+  // Remove |watch|. Returns true on success.
+  bool RemoveWatch(Watch watch, FilePathWatcherImpl* watcher);
+
+  // Callback for InotifyReaderTask.
+  void OnInotifyEvent(const inotify_event* event);
+
+ private:
+  friend struct ::base::DefaultLazyInstanceTraits<InotifyReader>;
+
+  typedef std::set<FilePathWatcherImpl*> WatcherSet;
+
+  InotifyReader();
+  ~InotifyReader();
+
+  // We keep track of which delegates want to be notified on which watches.
+  base::hash_map<Watch, WatcherSet> watchers_;
+
+  // Lock to protect watchers_.
+  base::Lock lock_;
+
+  // Separate thread on which we run blocking read for inotify events.
+  base::Thread thread_;
+
+  // File descriptor returned by inotify_init.
+  const int inotify_fd_;
+
+  // Use self-pipe trick to unblock select during shutdown.
+  int shutdown_pipe_[2];
+
+  // Flag set to true when startup was successful.
+  bool valid_;
+
+  DISALLOW_COPY_AND_ASSIGN(InotifyReader);
+};
+
+class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate,
+                            public MessageLoop::DestructionObserver {
+ public:
+  FilePathWatcherImpl();
+
+  // Called for each event coming from the watch. |fired_watch| identifies the
+  // watch that fired, |child| indicates what has changed, and is relative to
+  // the currently watched path for |fired_watch|. The flag |created| is true if
+  // the object appears, and |is_directory| is set when the event refers to a
+  // directory.
+  void OnFilePathChanged(InotifyReader::Watch fired_watch,
+                         const FilePath::StringType& child,
+                         bool created,
+                         bool is_directory);
+
+  // Start watching |path| for changes and notify |delegate| on each change.
+  // Returns true if watch for |path| has been added successfully.
+  virtual bool Watch(const FilePath& path,
+                     FilePathWatcher::Delegate* delegate) OVERRIDE;
+
+  // Cancel the watch. This unregisters the instance with InotifyReader.
+  virtual void Cancel() OVERRIDE;
+
+  // Deletion of the FilePathWatcher will call Cancel() to dispose of this
+  // object in the right thread. This also observes destruction of the required
+  // cleanup thread, in case it quits before Cancel() is called.
+  virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
+
+ private:
+  virtual ~FilePathWatcherImpl() {}
+
+  // Cleans up and stops observing the |message_loop_| thread.
+  void CancelOnMessageLoopThread() OVERRIDE;
+
+  // Inotify watches are installed for all directory components of |target_|. A
+  // WatchEntry instance holds the watch descriptor for a component and the
+  // subdirectory for that identifies the next component.
+  struct WatchEntry {
+    WatchEntry(InotifyReader::Watch watch, const FilePath::StringType& subdir)
+        : watch_(watch),
+          subdir_(subdir) {}
+
+    InotifyReader::Watch watch_;
+    FilePath::StringType subdir_;
+  };
+  typedef std::vector<WatchEntry> WatchVector;
+
+  // Reconfigure to watch for the most specific parent directory of |target_|
+  // that exists. Updates |watched_path_|. Returns true on success.
+  bool UpdateWatches() WARN_UNUSED_RESULT;
+
+  // Delegate to notify upon changes.
+  scoped_refptr<FilePathWatcher::Delegate> delegate_;
+
+  // The file or directory we're supposed to watch.
+  FilePath target_;
+
+  // The vector of watches and next component names for all path components,
+  // starting at the root directory. The last entry corresponds to the watch for
+  // |target_| and always stores an empty next component name in |subdir_|.
+  WatchVector watches_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
+};
+
+class InotifyReaderTask : public Task {
+ public:
+  InotifyReaderTask(InotifyReader* reader, int inotify_fd, int shutdown_fd)
+      : reader_(reader),
+        inotify_fd_(inotify_fd),
+        shutdown_fd_(shutdown_fd) {
+  }
+
+  virtual void Run() {
+    while (true) {
+      fd_set rfds;
+      FD_ZERO(&rfds);
+      FD_SET(inotify_fd_, &rfds);
+      FD_SET(shutdown_fd_, &rfds);
+
+      // Wait until some inotify events are available.
+      int select_result =
+        HANDLE_EINTR(select(std::max(inotify_fd_, shutdown_fd_) + 1,
+                            &rfds, NULL, NULL, NULL));
+      if (select_result < 0) {
+        DPLOG(WARNING) << "select failed";
+        return;
+      }
+
+      if (FD_ISSET(shutdown_fd_, &rfds))
+        return;
+
+      // Adjust buffer size to current event queue size.
+      int buffer_size;
+      int ioctl_result = HANDLE_EINTR(ioctl(inotify_fd_, FIONREAD,
+                                            &buffer_size));
+
+      if (ioctl_result != 0) {
+        DPLOG(WARNING) << "ioctl failed";
+        return;
+      }
+
+      std::vector<char> buffer(buffer_size);
+
+      ssize_t bytes_read = HANDLE_EINTR(read(inotify_fd_, &buffer[0],
+                                             buffer_size));
+
+      if (bytes_read < 0) {
+        DPLOG(WARNING) << "read from inotify fd failed";
+        return;
+      }
+
+      ssize_t i = 0;
+      while (i < bytes_read) {
+        inotify_event* event = reinterpret_cast<inotify_event*>(&buffer[i]);
+        size_t event_size = sizeof(inotify_event) + event->len;
+        DCHECK(i + event_size <= static_cast<size_t>(bytes_read));
+        reader_->OnInotifyEvent(event);
+        i += event_size;
+      }
+    }
+  }
+
+ private:
+  InotifyReader* reader_;
+  int inotify_fd_;
+  int shutdown_fd_;
+
+  DISALLOW_COPY_AND_ASSIGN(InotifyReaderTask);
+};
+
+static base::LazyInstance<InotifyReader> g_inotify_reader(
+    base::LINKER_INITIALIZED);
+
+InotifyReader::InotifyReader()
+    : thread_("inotify_reader"),
+      inotify_fd_(inotify_init()),
+      valid_(false) {
+  shutdown_pipe_[0] = -1;
+  shutdown_pipe_[1] = -1;
+  if (inotify_fd_ >= 0 && pipe(shutdown_pipe_) == 0 && thread_.Start()) {
+    thread_.message_loop()->PostTask(
+        FROM_HERE, new InotifyReaderTask(this, inotify_fd_, shutdown_pipe_[0]));
+    valid_ = true;
+  }
+}
+
+InotifyReader::~InotifyReader() {
+  if (valid_) {
+    // Write to the self-pipe so that the select call in InotifyReaderTask
+    // returns.
+    ssize_t ret = HANDLE_EINTR(write(shutdown_pipe_[1], "", 1));
+    DPCHECK(ret > 0);
+    DCHECK_EQ(ret, 1);
+    thread_.Stop();
+  }
+  if (inotify_fd_ >= 0)
+    close(inotify_fd_);
+  if (shutdown_pipe_[0] >= 0)
+    close(shutdown_pipe_[0]);
+  if (shutdown_pipe_[1] >= 0)
+    close(shutdown_pipe_[1]);
+}
+
+InotifyReader::Watch InotifyReader::AddWatch(
+    const FilePath& path, FilePathWatcherImpl* watcher) {
+  if (!valid_)
+    return kInvalidWatch;
+
+  base::AutoLock auto_lock(lock_);
+
+  Watch watch = inotify_add_watch(inotify_fd_, path.value().c_str(),
+                                  IN_CREATE | IN_DELETE |
+                                  IN_CLOSE_WRITE | IN_MOVE |
+                                  IN_ONLYDIR);
+
+  if (watch == kInvalidWatch)
+    return kInvalidWatch;
+
+  watchers_[watch].insert(watcher);
+
+  return watch;
+}
+
+bool InotifyReader::RemoveWatch(Watch watch,
+                                FilePathWatcherImpl* watcher) {
+  if (!valid_)
+    return false;
+
+  base::AutoLock auto_lock(lock_);
+
+  watchers_[watch].erase(watcher);
+
+  if (watchers_[watch].empty()) {
+    watchers_.erase(watch);
+    return (inotify_rm_watch(inotify_fd_, watch) == 0);
+  }
+
+  return true;
+}
+
+void InotifyReader::OnInotifyEvent(const inotify_event* event) {
+  if (event->mask & IN_IGNORED)
+    return;
+
+  FilePath::StringType child(event->len ? event->name : FILE_PATH_LITERAL(""));
+  base::AutoLock auto_lock(lock_);
+
+  for (WatcherSet::iterator watcher = watchers_[event->wd].begin();
+       watcher != watchers_[event->wd].end();
+       ++watcher) {
+    (*watcher)->OnFilePathChanged(event->wd,
+                                  child,
+                                  event->mask & (IN_CREATE | IN_MOVED_TO),
+                                  event->mask & IN_ISDIR);
+  }
+}
+
+FilePathWatcherImpl::FilePathWatcherImpl()
+    : delegate_(NULL) {
+}
+
+void FilePathWatcherImpl::OnFilePathChanged(
+    InotifyReader::Watch fired_watch,
+    const FilePath::StringType& child,
+    bool created,
+    bool is_directory) {
+
+  if (!message_loop()->BelongsToCurrentThread()) {
+    // Switch to message_loop_ to access watches_ safely.
+    message_loop()->PostTask(FROM_HERE,
+        NewRunnableMethod(this,
+                          &FilePathWatcherImpl::OnFilePathChanged,
+                          fired_watch,
+                          child,
+                          created,
+                          is_directory));
+    return;
+  }
+
+  DCHECK(MessageLoopForIO::current());
+
+  // Find the entry in |watches_| that corresponds to |fired_watch|.
+  WatchVector::const_iterator watch_entry(watches_.begin());
+  for ( ; watch_entry != watches_.end(); ++watch_entry) {
+    if (fired_watch == watch_entry->watch_)
+      break;
+  }
+
+  // If this notification is from a previous generation of watches or the watch
+  // has been cancelled (|watches_| is empty then), bail out.
+  if (watch_entry == watches_.end())
+    return;
+
+  // Check whether a path component of |target_| changed.
+  bool change_on_target_path = child.empty() || child == watch_entry->subdir_;
+
+  // Check whether the change references |target_| or a direct child.
+  DCHECK(watch_entry->subdir_.empty() || (watch_entry + 1) != watches_.end());
+  bool target_changed = watch_entry->subdir_.empty() ||
+      (watch_entry->subdir_ == child && (++watch_entry)->subdir_.empty());
+
+  // Update watches if a directory component of the |target_| path (dis)appears.
+  if (is_directory && change_on_target_path && !UpdateWatches()) {
+    delegate_->OnFilePathError(target_);
+    return;
+  }
+
+  // Report the following events:
+  //  - The target or a direct child of the target got changed (in case the
+  //    watched path refers to a directory).
+  //  - One of the parent directories got moved or deleted, since the target
+  //    disappears in this case.
+  //  - One of the parent directories appears. The event corresponding to the
+  //    target appearing might have been missed in this case, so recheck.
+  if (target_changed ||
+      (change_on_target_path && !created) ||
+      (change_on_target_path && file_util::PathExists(target_))) {
+    delegate_->OnFilePathChanged(target_);
+  }
+}
+
+bool FilePathWatcherImpl::Watch(const FilePath& path,
+                                FilePathWatcher::Delegate* delegate) {
+  DCHECK(target_.empty());
+  DCHECK(MessageLoopForIO::current());
+
+  set_message_loop(base::MessageLoopProxy::CreateForCurrentThread());
+  delegate_ = delegate;
+  target_ = path;
+  MessageLoop::current()->AddDestructionObserver(this);
+
+  std::vector<FilePath::StringType> comps;
+  target_.GetComponents(&comps);
+  DCHECK(!comps.empty());
+  for (std::vector<FilePath::StringType>::const_iterator comp(++comps.begin());
+       comp != comps.end(); ++comp) {
+    watches_.push_back(WatchEntry(InotifyReader::kInvalidWatch, *comp));
+  }
+  watches_.push_back(WatchEntry(InotifyReader::kInvalidWatch,
+                                FilePath::StringType()));
+  return UpdateWatches();
+}
+
+void FilePathWatcherImpl::Cancel() {
+  if (!delegate_) {
+    // Watch was never called, or the |message_loop_| thread is already gone.
+    set_cancelled();
+    return;
+  }
+
+  // Switch to the message_loop_ if necessary so we can access |watches_|.
+  if (!message_loop()->BelongsToCurrentThread()) {
+    message_loop()->PostTask(FROM_HERE,
+                             new FilePathWatcher::CancelTask(this));
+  } else {
+    CancelOnMessageLoopThread();
+  }
+}
+
+void FilePathWatcherImpl::CancelOnMessageLoopThread() {
+  if (!is_cancelled()) {
+    set_cancelled();
+    MessageLoop::current()->RemoveDestructionObserver(this);
+
+    for (WatchVector::iterator watch_entry(watches_.begin());
+         watch_entry != watches_.end(); ++watch_entry) {
+      if (watch_entry->watch_ != InotifyReader::kInvalidWatch)
+        g_inotify_reader.Get().RemoveWatch(watch_entry->watch_, this);
+    }
+    watches_.clear();
+    delegate_ = NULL;
+    target_.clear();
+  }
+}
+
+void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
+  CancelOnMessageLoopThread();
+}
+
+bool FilePathWatcherImpl::UpdateWatches() {
+  // Ensure this runs on the message_loop_ exclusively in order to avoid
+  // concurrency issues.
+  DCHECK(message_loop()->BelongsToCurrentThread());
+
+  // Walk the list of watches and update them as we go.
+  FilePath path(FILE_PATH_LITERAL("/"));
+  bool path_valid = true;
+  for (WatchVector::iterator watch_entry(watches_.begin());
+       watch_entry != watches_.end(); ++watch_entry) {
+    InotifyReader::Watch old_watch = watch_entry->watch_;
+    if (path_valid) {
+      watch_entry->watch_ = g_inotify_reader.Get().AddWatch(path, this);
+      if (watch_entry->watch_ == InotifyReader::kInvalidWatch) {
+        path_valid = false;
+      }
+    } else {
+      watch_entry->watch_ = InotifyReader::kInvalidWatch;
+    }
+    if (old_watch != InotifyReader::kInvalidWatch &&
+        old_watch != watch_entry->watch_) {
+      g_inotify_reader.Get().RemoveWatch(old_watch, this);
+    }
+    path = path.Append(watch_entry->subdir_);
+  }
+
+  return true;
+}
+
+}  // namespace
+
+FilePathWatcher::FilePathWatcher() {
+  impl_ = new FilePathWatcherImpl();
+}
+
+}  // namespace files
+}  // namespace base
diff --git a/base/files/file_path_watcher_mac.cc b/base/files/file_path_watcher_mac.cc
new file mode 100644
index 0000000..7b61f76
--- /dev/null
+++ b/base/files/file_path_watcher_mac.cc
@@ -0,0 +1,493 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/files/file_path_watcher.h"
+
+#include <fcntl.h>
+#include <sys/event.h>
+#include <sys/param.h>
+
+#include <vector>
+
+#include "base/file_util.h"
+#include "base/message_loop.h"
+#include "base/message_loop_proxy.h"
+#include "base/stringprintf.h"
+
+namespace base {
+namespace files {
+
+namespace {
+
+// Mac-specific file watcher implementation based on kqueue.
+// Originally it was based on FSEvents so that the semantics were equivalent
+// on Linux, OSX and Windows where it was able to detect:
+// - file creation/deletion/modification in a watched directory
+// - file creation/deletion/modification for a watched file
+// - modifications to the paths to a watched object that would affect the
+//   object such as renaming/attibute changes etc.
+// The FSEvents version did all of the above except handling attribute changes
+// to path components. Unfortunately FSEvents appears to have an issue where the
+// current implementation (Mac OS X 10.6.7) sometimes drops events and doesn't
+// send notifications. See
+// http://code.google.com/p/chromium/issues/detail?id=54822#c31 for source that
+// will reproduce the problem. FSEvents also required having a CFRunLoop
+// backing the thread that it was running on, that caused added complexity
+// in the interfaces.
+// The kqueue implementation will handle all of the items in the list above
+// except for detecting modifications to files in a watched directory. It will
+// detect the creation and deletion of files, just not the modification of
+// files. It does however detect the attribute changes that the FSEvents impl
+// would miss.
+class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate,
+                            public MessageLoopForIO::Watcher,
+                            public MessageLoop::DestructionObserver {
+ public:
+  FilePathWatcherImpl() : kqueue_(-1) {}
+  virtual ~FilePathWatcherImpl() {}
+
+  // MessageLoopForIO::Watcher overrides.
+  virtual void OnFileCanReadWithoutBlocking(int fd) OVERRIDE;
+  virtual void OnFileCanWriteWithoutBlocking(int fd) OVERRIDE;
+
+  // MessageLoop::DestructionObserver overrides.
+  virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
+
+  // FilePathWatcher::PlatformDelegate overrides.
+  virtual bool Watch(const FilePath& path,
+                     FilePathWatcher::Delegate* delegate) OVERRIDE;
+  virtual void Cancel() OVERRIDE;
+
+ private:
+  class EventData {
+   public:
+    EventData(const FilePath& path, const FilePath::StringType& subdir)
+        : path_(path), subdir_(subdir) { }
+    FilePath path_;  // Full path to this item.
+    FilePath::StringType subdir_;  // Path to any sub item.
+  };
+  typedef std::vector<struct kevent> EventVector;
+
+  // Can only be called on |io_message_loop_|'s thread.
+  virtual void CancelOnMessageLoopThread() OVERRIDE;
+
+  // Returns true if the kevent values are error free.
+  bool AreKeventValuesValid(struct kevent* kevents, int count);
+
+  // Respond to a change of attributes of the path component represented by
+  // |event|. Sets |target_file_affected| to true if |target_| is affected.
+  // Sets |update_watches| to true if |events_| need to be updated.
+  void HandleAttributesChange(const EventVector::iterator& event,
+                              bool* target_file_affected,
+                              bool* update_watches);
+
+  // Respond to a move of deletion of the path component represented by
+  // |event|. Sets |target_file_affected| to true if |target_| is affected.
+  // Sets |update_watches| to true if |events_| need to be updated.
+  void HandleDeleteOrMoveChange(const EventVector::iterator& event,
+                                bool* target_file_affected,
+                                bool* update_watches);
+
+  // Respond to a creation of an item in the path component represented by
+  // |event|. Sets |target_file_affected| to true if |target_| is affected.
+  // Sets |update_watches| to true if |events_| need to be updated.
+  void HandleCreateItemChange(const EventVector::iterator& event,
+                              bool* target_file_affected,
+                              bool* update_watches);
+
+  // Update |events_| with the current status of the system.
+  // Sets |target_file_affected| to true if |target_| is affected.
+  // Returns false if an error occurs.
+  bool UpdateWatches(bool* target_file_affected);
+
+  // Fills |events| with one kevent per component in |path|.
+  // Returns the number of valid events created where a valid event is
+  // defined as one that has a ident (file descriptor) field != -1.
+  static int EventsForPath(FilePath path, EventVector *events);
+
+  // Release a kevent generated by EventsForPath.
+  static void ReleaseEvent(struct kevent& event);
+
+  // Returns a file descriptor that will not block the system from deleting
+  // the file it references.
+  static int FileDescriptorForPath(const FilePath& path);
+
+  // Closes |*fd| and sets |*fd| to -1.
+  static void CloseFileDescriptor(int* fd);
+
+  // Returns true if kevent has open file descriptor.
+  static bool IsKeventFileDescriptorOpen(const struct kevent& event) {
+    return event.ident != static_cast<uintptr_t>(-1);
+  }
+
+  static EventData* EventDataForKevent(const struct kevent& event) {
+    return reinterpret_cast<EventData*>(event.udata);
+  }
+
+  EventVector events_;
+  scoped_refptr<base::MessageLoopProxy> io_message_loop_;
+  MessageLoopForIO::FileDescriptorWatcher kqueue_watcher_;
+  scoped_refptr<FilePathWatcher::Delegate> delegate_;
+  FilePath target_;
+  int kqueue_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
+};
+
+void FilePathWatcherImpl::ReleaseEvent(struct kevent& event) {
+  CloseFileDescriptor(reinterpret_cast<int*>(&event.ident));
+  EventData* entry = EventDataForKevent(event);
+  delete entry;
+  event.udata = NULL;
+}
+
+int FilePathWatcherImpl::EventsForPath(FilePath path, EventVector* events) {
+  DCHECK(MessageLoopForIO::current());
+  // Make sure that we are working with a clean slate.
+  DCHECK(events->empty());
+
+  std::vector<FilePath::StringType> components;
+  path.GetComponents(&components);
+
+  if (components.size() < 1) {
+    return -1;
+  }
+
+  int last_existing_entry = 0;
+  FilePath built_path;
+  bool path_still_exists = true;
+  for(std::vector<FilePath::StringType>::iterator i = components.begin();
+      i != components.end(); ++i) {
+    if (i == components.begin()) {
+      built_path = FilePath(*i);
+    } else {
+      built_path = built_path.Append(*i);
+    }
+    int fd = -1;
+    if (path_still_exists) {
+      fd = FileDescriptorForPath(built_path);
+      if (fd == -1) {
+        path_still_exists = false;
+      } else {
+        ++last_existing_entry;
+      }
+    }
+    FilePath::StringType subdir = (i != (components.end() - 1)) ? *(i + 1) : "";
+    EventData* data = new EventData(built_path, subdir);
+    struct kevent event;
+    EV_SET(&event, fd, EVFILT_VNODE, (EV_ADD | EV_CLEAR | EV_RECEIPT),
+           (NOTE_DELETE | NOTE_WRITE | NOTE_ATTRIB |
+            NOTE_RENAME | NOTE_REVOKE | NOTE_EXTEND), 0, data);
+    events->push_back(event);
+  }
+  return last_existing_entry;
+}
+
+int FilePathWatcherImpl::FileDescriptorForPath(const FilePath& path) {
+  return HANDLE_EINTR(open(path.value().c_str(), O_EVTONLY));
+}
+
+void FilePathWatcherImpl::CloseFileDescriptor(int *fd) {
+  if (*fd == -1) {
+    return;
+  }
+
+  if (HANDLE_EINTR(close(*fd)) != 0) {
+    PLOG(ERROR) << "close";
+  }
+  *fd = -1;
+}
+
+bool FilePathWatcherImpl::AreKeventValuesValid(struct kevent* kevents,
+                                               int count) {
+  if (count < 0) {
+    PLOG(ERROR) << "kevent";
+    return false;
+  }
+  bool valid = true;
+  for (int i = 0; i < count; ++i) {
+    if (kevents[i].flags & EV_ERROR && kevents[i].data) {
+      // Find the kevent in |events_| that matches the kevent with the error.
+      EventVector::iterator event = events_.begin();
+      for (; event != events_.end(); ++event) {
+        if (event->ident == kevents[i].ident) {
+          break;
+        }
+      }
+      std::string path_name;
+      if (event != events_.end()) {
+        EventData* event_data = EventDataForKevent(*event);
+        if (event_data != NULL) {
+          path_name = event_data->path_.value();
+        }
+      }
+      if (path_name.empty()) {
+        path_name = base::StringPrintf(
+            "fd %d", *reinterpret_cast<int*>(&kevents[i].ident));
+      }
+      LOG(ERROR) << "Error: " << kevents[i].data << " for " << path_name;
+      valid = false;
+    }
+  }
+  return valid;
+}
+
+void FilePathWatcherImpl::HandleAttributesChange(
+    const EventVector::iterator& event,
+    bool* target_file_affected,
+    bool* update_watches) {
+  EventVector::iterator next_event = event + 1;
+  EventData* next_event_data = EventDataForKevent(*next_event);
+  // Check to see if the next item in path is still accessible.
+  int have_access = FileDescriptorForPath(next_event_data->path_);
+  if (have_access == -1) {
+    *target_file_affected = true;
+    *update_watches = true;
+    EventVector::iterator local_event(event);
+    for (; local_event != events_.end(); ++local_event) {
+      // Close all nodes from the event down. This has the side effect of
+      // potentially rendering other events in |updates| invalid.
+      // There is no need to remove the events from |kqueue_| because this
+      // happens as a side effect of closing the file descriptor.
+      CloseFileDescriptor(reinterpret_cast<int*>(&local_event->ident));
+    }
+  } else {
+    CloseFileDescriptor(&have_access);
+  }
+}
+
+void FilePathWatcherImpl::HandleDeleteOrMoveChange(
+    const EventVector::iterator& event,
+    bool* target_file_affected,
+    bool* update_watches) {
+  *target_file_affected = true;
+  *update_watches = true;
+  EventVector::iterator local_event(event);
+  for (; local_event != events_.end(); ++local_event) {
+    // Close all nodes from the event down. This has the side effect of
+    // potentially rendering other events in |updates| invalid.
+    // There is no need to remove the events from |kqueue_| because this
+    // happens as a side effect of closing the file descriptor.
+    CloseFileDescriptor(reinterpret_cast<int*>(&local_event->ident));
+  }
+}
+
+void FilePathWatcherImpl::HandleCreateItemChange(
+    const EventVector::iterator& event,
+    bool* target_file_affected,
+    bool* update_watches) {
+  // Get the next item in the path.
+  EventVector::iterator next_event = event + 1;
+  EventData* next_event_data = EventDataForKevent(*next_event);
+
+  // Check to see if it already has a valid file descriptor.
+  if (!IsKeventFileDescriptorOpen(*next_event)) {
+    // If not, attempt to open a file descriptor for it.
+    next_event->ident = FileDescriptorForPath(next_event_data->path_);
+    if (IsKeventFileDescriptorOpen(*next_event)) {
+      *update_watches = true;
+      if (next_event_data->subdir_.empty()) {
+        *target_file_affected = true;
+      }
+    }
+  }
+}
+
+bool FilePathWatcherImpl::UpdateWatches(bool* target_file_affected) {
+  // Iterate over events adding kevents for items that exist to the kqueue.
+  // Then check to see if new components in the path have been created.
+  // Repeat until no new components in the path are detected.
+  // This is to get around races in directory creation in a watched path.
+  bool update_watches = true;
+  while (update_watches) {
+    size_t valid;
+    for (valid = 0; valid < events_.size(); ++valid) {
+      if (!IsKeventFileDescriptorOpen(events_[valid])) {
+        break;
+      }
+    }
+    if (valid == 0) {
+      // The root of the file path is inaccessible?
+      return false;
+    }
+
+    EventVector updates(valid);
+    int count = HANDLE_EINTR(kevent(kqueue_, &events_[0], valid, &updates[0],
+                                    valid, NULL));
+    if (!AreKeventValuesValid(&updates[0], count)) {
+      return false;
+    }
+    update_watches = false;
+    for (; valid < events_.size(); ++valid) {
+      EventData* event_data = EventDataForKevent(events_[valid]);
+      events_[valid].ident = FileDescriptorForPath(event_data->path_);
+      if (IsKeventFileDescriptorOpen(events_[valid])) {
+        update_watches = true;
+        if (event_data->subdir_.empty()) {
+          *target_file_affected = true;
+        }
+      } else {
+        break;
+      }
+    }
+  }
+  return true;
+}
+
+void FilePathWatcherImpl::OnFileCanReadWithoutBlocking(int fd) {
+  DCHECK(MessageLoopForIO::current());
+  CHECK_EQ(fd, kqueue_);
+  CHECK(events_.size());
+
+  // Request the file system update notifications that have occurred and return
+  // them in |updates|. |count| will contain the number of updates that have
+  // occurred.
+  EventVector updates(events_.size());
+  struct timespec timeout = {0, 0};
+  int count = HANDLE_EINTR(kevent(kqueue_, NULL, 0, &updates[0], updates.size(),
+                                  &timeout));
+
+  // Error values are stored within updates, so check to make sure that no
+  // errors occurred.
+  if (!AreKeventValuesValid(&updates[0], count)) {
+    delegate_->OnFilePathError(target_);
+    Cancel();
+    return;
+  }
+
+  bool update_watches = false;
+  bool send_notification = false;
+
+  // Iterate through each of the updates and react to them.
+  for (int i = 0; i < count; ++i) {
+    // Find our kevent record that matches the update notification.
+    EventVector::iterator event = events_.begin();
+    for (; event != events_.end(); ++event) {
+      if (!IsKeventFileDescriptorOpen(*event) ||
+          event->ident == updates[i].ident) {
+        break;
+      }
+    }
+    if (!IsKeventFileDescriptorOpen(*event) || event == events_.end()) {
+      // The event may no longer exist in |events_| because another event
+      // modified |events_| in such a way to make it invalid. For example if
+      // the path is /foo/bar/bam and foo is deleted, NOTE_DELETE events for
+      // foo, bar and bam will be sent. If foo is processed first, then
+      // the file descriptors for bar and bam will already be closed and set
+      // to -1 before they get a chance to be processed.
+      continue;
+    }
+
+    EventData* event_data = EventDataForKevent(*event);
+
+    // If the subdir is empty, this is the last item on the path and is the
+    // target file.
+    bool target_file_affected = event_data->subdir_.empty();
+    if ((updates[i].fflags & NOTE_ATTRIB) && !target_file_affected) {
+      HandleAttributesChange(event, &target_file_affected, &update_watches);
+    }
+    if (updates[i].fflags & (NOTE_DELETE | NOTE_REVOKE | NOTE_RENAME)) {
+      HandleDeleteOrMoveChange(event, &target_file_affected, &update_watches);
+    }
+    if ((updates[i].fflags & NOTE_WRITE) && !target_file_affected) {
+      HandleCreateItemChange(event, &target_file_affected, &update_watches);
+    }
+    send_notification |= target_file_affected;
+  }
+
+  if (update_watches) {
+    if (!UpdateWatches(&send_notification)) {
+      delegate_->OnFilePathError(target_);
+      Cancel();
+    }
+  }
+
+  if (send_notification) {
+    delegate_->OnFilePathChanged(target_);
+  }
+}
+
+void FilePathWatcherImpl::OnFileCanWriteWithoutBlocking(int fd) {
+  NOTREACHED();
+}
+
+void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
+  CancelOnMessageLoopThread();
+}
+
+bool FilePathWatcherImpl::Watch(const FilePath& path,
+                                FilePathWatcher::Delegate* delegate) {
+  DCHECK(MessageLoopForIO::current());
+  DCHECK(target_.value().empty());  // Can only watch one path.
+  DCHECK(delegate);
+  DCHECK_EQ(kqueue_, -1);
+
+  delegate_ = delegate;
+  target_ = path;
+
+  MessageLoop::current()->AddDestructionObserver(this);
+  io_message_loop_ = base::MessageLoopProxy::CreateForCurrentThread();
+
+  kqueue_ = kqueue();
+  if (kqueue_ == -1) {
+    PLOG(ERROR) << "kqueue";
+    return false;
+  }
+
+  int last_entry = EventsForPath(target_, &events_);
+  CHECK_NE(last_entry, 0);
+
+  EventVector responses(last_entry);
+
+  int count = HANDLE_EINTR(kevent(kqueue_, &events_[0], last_entry,
+                                  &responses[0], last_entry, NULL));
+  if (!AreKeventValuesValid(&responses[0], count)) {
+    // Calling Cancel() here to close any file descriptors that were opened.
+    // This would happen in the destructor anyways, but FilePathWatchers tend to
+    // be long lived, and if an error has occurred, there is no reason to waste
+    // the file descriptors.
+    Cancel();
+    return false;
+  }
+
+  return MessageLoopForIO::current()->WatchFileDescriptor(
+      kqueue_, true, MessageLoopForIO::WATCH_READ, &kqueue_watcher_, this);
+}
+
+void FilePathWatcherImpl::Cancel() {
+  base::MessageLoopProxy* proxy = io_message_loop_.get();
+  if (!proxy) {
+    set_cancelled();
+    return;
+  }
+  if (!proxy->BelongsToCurrentThread()) {
+    proxy->PostTask(FROM_HERE,
+                    NewRunnableMethod(this, &FilePathWatcherImpl::Cancel));
+    return;
+  }
+  CancelOnMessageLoopThread();
+}
+
+void FilePathWatcherImpl::CancelOnMessageLoopThread() {
+  DCHECK(MessageLoopForIO::current());
+  if (!is_cancelled()) {
+    set_cancelled();
+    kqueue_watcher_.StopWatchingFileDescriptor();
+    CloseFileDescriptor(&kqueue_);
+    std::for_each(events_.begin(), events_.end(), ReleaseEvent);
+    events_.clear();
+    io_message_loop_ = NULL;
+    MessageLoop::current()->RemoveDestructionObserver(this);
+    delegate_ = NULL;
+  }
+}
+
+}  // namespace
+
+FilePathWatcher::FilePathWatcher() {
+  impl_ = new FilePathWatcherImpl();
+}
+
+}  // namespace files
+}  // namespace base
diff --git a/base/files/file_path_watcher_stub.cc b/base/files/file_path_watcher_stub.cc
new file mode 100644
index 0000000..a693dc7
--- /dev/null
+++ b/base/files/file_path_watcher_stub.cc
@@ -0,0 +1,31 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This file exists for Unix systems which don't have the inotify headers, and
+// thus cannot build file_watcher_inotify.cc
+
+#include "base/files/file_path_watcher.h"
+
+namespace base {
+namespace files {
+
+namespace {
+
+class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate {
+ public:
+  virtual bool Watch(const FilePath& path,
+                     FileWatcher::Delegate* delegate,
+                     base::MessageLoopProxy*) OVERRIDE {
+    return false;
+  }
+};
+
+}  // namespace
+
+FilePathWatcher::FilePathWatcher() {
+  impl_ = new FilePathWatcherImpl();
+}
+
+}  // namespace files
+}  // namespace base
diff --git a/base/files/file_path_watcher_win.cc b/base/files/file_path_watcher_win.cc
new file mode 100644
index 0000000..eedcf22
--- /dev/null
+++ b/base/files/file_path_watcher_win.cc
@@ -0,0 +1,281 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/files/file_path_watcher.h"
+
+#include "base/file_path.h"
+#include "base/file_util.h"
+#include "base/logging.h"
+#include "base/memory/ref_counted.h"
+#include "base/message_loop_proxy.h"
+#include "base/time.h"
+#include "base/win/object_watcher.h"
+
+namespace base {
+namespace files {
+
+namespace {
+
+class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate,
+                            public base::win::ObjectWatcher::Delegate,
+                            public MessageLoop::DestructionObserver {
+ public:
+  FilePathWatcherImpl() : delegate_(NULL), handle_(INVALID_HANDLE_VALUE) {}
+
+  // FilePathWatcher::PlatformDelegate overrides.
+  virtual bool Watch(const FilePath& path,
+                     FilePathWatcher::Delegate* delegate) OVERRIDE;
+  virtual void Cancel() OVERRIDE;
+
+  // Deletion of the FilePathWatcher will call Cancel() to dispose of this
+  // object in the right thread. This also observes destruction of the required
+  // cleanup thread, in case it quits before Cancel() is called.
+  virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
+
+  // Callback from MessageLoopForIO.
+  virtual void OnObjectSignaled(HANDLE object);
+
+ private:
+  virtual ~FilePathWatcherImpl() {}
+
+  // Setup a watch handle for directory |dir|. Returns true if no fatal error
+  // occurs. |handle| will receive the handle value if |dir| is watchable,
+  // otherwise INVALID_HANDLE_VALUE.
+  static bool SetupWatchHandle(const FilePath& dir, HANDLE* handle)
+      WARN_UNUSED_RESULT;
+
+  // (Re-)Initialize the watch handle.
+  bool UpdateWatch() WARN_UNUSED_RESULT;
+
+  // Destroy the watch handle.
+  void DestroyWatch();
+
+  // Cleans up and stops observing the |message_loop_| thread.
+  void CancelOnMessageLoopThread() OVERRIDE;
+
+  // Delegate to notify upon changes.
+  scoped_refptr<FilePathWatcher::Delegate> delegate_;
+
+  // Path we're supposed to watch (passed to delegate).
+  FilePath target_;
+
+  // Handle for FindFirstChangeNotification.
+  HANDLE handle_;
+
+  // ObjectWatcher to watch handle_ for events.
+  base::win::ObjectWatcher watcher_;
+
+  // Keep track of the last modified time of the file.  We use nulltime
+  // to represent the file not existing.
+  base::Time last_modified_;
+
+  // The time at which we processed the first notification with the
+  // |last_modified_| time stamp.
+  base::Time first_notification_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
+};
+
+bool FilePathWatcherImpl::Watch(const FilePath& path,
+                                FilePathWatcher::Delegate* delegate) {
+  DCHECK(target_.value().empty());  // Can only watch one path.
+
+  set_message_loop(base::MessageLoopProxy::CreateForCurrentThread());
+  delegate_ = delegate;
+  target_ = path;
+  MessageLoop::current()->AddDestructionObserver(this);
+
+  if (!UpdateWatch())
+    return false;
+
+  watcher_.StartWatching(handle_, this);
+
+  return true;
+}
+
+void FilePathWatcherImpl::Cancel() {
+  if (!delegate_) {
+    // Watch was never called, or the |message_loop_| has already quit.
+    set_cancelled();
+    return;
+  }
+
+  // Switch to the file thread if necessary so we can stop |watcher_|.
+  if (!message_loop()->BelongsToCurrentThread()) {
+    message_loop()->PostTask(FROM_HERE,
+                             new FilePathWatcher::CancelTask(this));
+  } else {
+    CancelOnMessageLoopThread();
+  }
+}
+
+void FilePathWatcherImpl::CancelOnMessageLoopThread() {
+  set_cancelled();
+
+  if (handle_ != INVALID_HANDLE_VALUE)
+    DestroyWatch();
+
+  if (delegate_) {
+    MessageLoop::current()->RemoveDestructionObserver(this);
+    delegate_ = NULL;
+  }
+}
+
+void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
+  CancelOnMessageLoopThread();
+}
+
+void FilePathWatcherImpl::OnObjectSignaled(HANDLE object) {
+  DCHECK(object == handle_);
+  // Make sure we stay alive through the body of this function.
+  scoped_refptr<FilePathWatcherImpl> keep_alive(this);
+
+  if (!UpdateWatch()) {
+    delegate_->OnFilePathError(target_);
+    return;
+  }
+
+  // Check whether the event applies to |target_| and notify the delegate.
+  base::PlatformFileInfo file_info;
+  bool file_exists = file_util::GetFileInfo(target_, &file_info);
+  if (file_exists && (last_modified_.is_null() ||
+      last_modified_ != file_info.last_modified)) {
+    last_modified_ = file_info.last_modified;
+    first_notification_ = base::Time::Now();
+    delegate_->OnFilePathChanged(target_);
+  } else if (file_exists && !first_notification_.is_null()) {
+    // The target's last modification time is equal to what's on record. This
+    // means that either an unrelated event occurred, or the target changed
+    // again (file modification times only have a resolution of 1s). Comparing
+    // file modification times against the wall clock is not reliable to find
+    // out whether the change is recent, since this code might just run too
+    // late. Moreover, there's no guarantee that file modification time and wall
+    // clock times come from the same source.
+    //
+    // Instead, the time at which the first notification carrying the current
+    // |last_notified_| time stamp is recorded. Later notifications that find
+    // the same file modification time only need to be forwarded until wall
+    // clock has advanced one second from the initial notification. After that
+    // interval, client code is guaranteed to having seen the current revision
+    // of the file.
+    if (base::Time::Now() - first_notification_ >
+        base::TimeDelta::FromSeconds(1)) {
+      // Stop further notifications for this |last_modification_| time stamp.
+      first_notification_ = base::Time();
+    }
+    delegate_->OnFilePathChanged(target_);
+  } else if (!file_exists && !last_modified_.is_null()) {
+    last_modified_ = base::Time();
+    delegate_->OnFilePathChanged(target_);
+  }
+
+  // The watch may have been cancelled by the callback.
+  if (handle_ != INVALID_HANDLE_VALUE)
+    watcher_.StartWatching(handle_, this);
+}
+
+// static
+bool FilePathWatcherImpl::SetupWatchHandle(const FilePath& dir,
+                                           HANDLE* handle) {
+  *handle = FindFirstChangeNotification(
+      dir.value().c_str(),
+      false,  // Don't watch subtrees
+      FILE_NOTIFY_CHANGE_FILE_NAME | FILE_NOTIFY_CHANGE_SIZE |
+      FILE_NOTIFY_CHANGE_LAST_WRITE | FILE_NOTIFY_CHANGE_DIR_NAME |
+      FILE_NOTIFY_CHANGE_ATTRIBUTES | FILE_NOTIFY_CHANGE_SECURITY);
+  if (*handle != INVALID_HANDLE_VALUE) {
+    // Make sure the handle we got points to an existing directory. It seems
+    // that windows sometimes hands out watches to direectories that are
+    // about to go away, but doesn't sent notifications if that happens.
+    if (!file_util::DirectoryExists(dir)) {
+      FindCloseChangeNotification(*handle);
+      *handle = INVALID_HANDLE_VALUE;
+    }
+    return true;
+  }
+
+  // If FindFirstChangeNotification failed because the target directory
+  // doesn't exist, access is denied (happens if the file is already gone but
+  // there are still handles open), or the target is not a directory, try the
+  // immediate parent directory instead.
+  DWORD error_code = GetLastError();
+  if (error_code != ERROR_FILE_NOT_FOUND &&
+      error_code != ERROR_PATH_NOT_FOUND &&
+      error_code != ERROR_ACCESS_DENIED &&
+      error_code != ERROR_SHARING_VIOLATION &&
+      error_code != ERROR_DIRECTORY) {
+    using ::operator<<; // Pick the right operator<< below.
+    PLOG(ERROR) << "FindFirstChangeNotification failed for "
+                << dir.value();
+    return false;
+  }
+
+  return true;
+}
+
+bool FilePathWatcherImpl::UpdateWatch() {
+  if (handle_ != INVALID_HANDLE_VALUE)
+    DestroyWatch();
+
+  base::PlatformFileInfo file_info;
+  if (file_util::GetFileInfo(target_, &file_info)) {
+    last_modified_ = file_info.last_modified;
+    first_notification_ = base::Time::Now();
+  }
+
+  // Start at the target and walk up the directory chain until we succesfully
+  // create a watch handle in |handle_|. |child_dirs| keeps a stack of child
+  // directories stripped from target, in reverse order.
+  std::vector<FilePath> child_dirs;
+  FilePath watched_path(target_);
+  while (true) {
+    if (!SetupWatchHandle(watched_path, &handle_))
+      return false;
+
+    // Break if a valid handle is returned. Try the parent directory otherwise.
+    if (handle_ != INVALID_HANDLE_VALUE)
+      break;
+
+    // Abort if we hit the root directory.
+    child_dirs.push_back(watched_path.BaseName());
+    FilePath parent(watched_path.DirName());
+    if (parent == watched_path) {
+      LOG(ERROR) << "Reached the root directory";
+      return false;
+    }
+    watched_path = parent;
+  }
+
+  // At this point, handle_ is valid. However, the bottom-up search that the
+  // above code performs races against directory creation. So try to walk back
+  // down and see whether any children appeared in the mean time.
+  while (!child_dirs.empty()) {
+    watched_path = watched_path.Append(child_dirs.back());
+    child_dirs.pop_back();
+    HANDLE temp_handle = INVALID_HANDLE_VALUE;
+    if (!SetupWatchHandle(watched_path, &temp_handle))
+      return false;
+    if (temp_handle == INVALID_HANDLE_VALUE)
+      break;
+    FindCloseChangeNotification(handle_);
+    handle_ = temp_handle;
+  }
+
+  return true;
+}
+
+void FilePathWatcherImpl::DestroyWatch() {
+  watcher_.StopWatching();
+  FindCloseChangeNotification(handle_);
+  handle_ = INVALID_HANDLE_VALUE;
+}
+
+}  // namespace
+
+FilePathWatcher::FilePathWatcher() {
+  impl_ = new FilePathWatcherImpl();
+}
+
+}  // namespace files
+}  // namespace base