app_shell: Fix crash on chrome.runtime.getPackageDirectoryEntry for cros

Because app_shell does not support code in //chrome it cannot register the
special chromeos::FileSystemBackend that handles kFileSystemTypeNativeLocal.
However, code in //storage in IsolatedFileSystemBackend implicitly assumes
that on Chrome OS kFileSystemTypeNativeLocal will be handled elsewhere.

This patch changes IsolatedFileSystemBackend to provide support for
kFileSystemTypeNativeLocal whenever the //storage embedder does not provide a
backend for it. This preserves existing behavior for non-app_shell platforms
and makes app_shell behave like Linux, which works fine.

A better solution would be to refactor chromeos::FileSystemBackend out of
//chrome/browser/chromeos, but that is blocked on componentization of
//chrome/browser/drive, see http://crbug.com/257943

BUG=447027
TEST=existing FileSystem unit and browser tests, manual test of app_shell (see bug for test app)

Review URL: https://codereview.chromium.org/838323003

Cr-Commit-Position: refs/heads/master@{#310780}

3 files changed, 28 insertions, 8 deletions

diff --git a/storage/browser/fileapi/file_system_context.cc b/storage/browser/fileapi/file_system_context.cc
index 4b300ef..85a9317 100644
--- a/storage/browser/fileapi/file_system_context.cc
+++ b/storage/browser/fileapi/file_system_context.cc
@@ -150,7 +150,6 @@ FileSystemContext::FileSystemContext(
                                                special_storage_policy,
                                                options)),
       sandbox_backend_(new SandboxFileSystemBackend(sandbox_delegate_.get())),
-      isolated_backend_(new IsolatedFileSystemBackend()),
       plugin_private_backend_(
           new PluginPrivateFileSystemBackend(file_task_runner,
                                              partition_path,
@@ -163,7 +162,6 @@ FileSystemContext::FileSystemContext(
       is_incognito_(options.is_incognito()),
       operation_runner_(new FileSystemOperationRunner(this)) {
   RegisterBackend(sandbox_backend_.get());
-  RegisterBackend(isolated_backend_.get());
   RegisterBackend(plugin_private_backend_.get());
 
   for (ScopedVector<FileSystemBackend>::const_iterator iter =
@@ -172,6 +170,16 @@ FileSystemContext::FileSystemContext(
     RegisterBackend(*iter);
   }
 
+  // If the embedder's additional backends already provide support for
+  // kFileSystemTypeNativeLocal and kFileSystemTypeNativeForPlatformApp then
+  // IsolatedFileSystemBackend does not need to handle them. For example, on
+  // Chrome OS the additional backend chromeos::FileSystemBackend handles these
+  // types.
+  isolated_backend_.reset(new IsolatedFileSystemBackend(
+      !ContainsKey(backend_map_, kFileSystemTypeNativeLocal),
+      !ContainsKey(backend_map_, kFileSystemTypeNativeForPlatformApp)));
+  RegisterBackend(isolated_backend_.get());
+
   if (quota_manager_proxy) {
     // Quota client assumes all backends have registered.
     quota_manager_proxy->RegisterClient(CreateQuotaClient(
diff --git a/storage/browser/fileapi/isolated_file_system_backend.cc b/storage/browser/fileapi/isolated_file_system_backend.cc
index c9b31d3..823d404 100644
--- a/storage/browser/fileapi/isolated_file_system_backend.cc
+++ b/storage/browser/fileapi/isolated_file_system_backend.cc
@@ -29,8 +29,12 @@
 
 namespace storage {
 
-IsolatedFileSystemBackend::IsolatedFileSystemBackend()
-    : isolated_file_util_(new AsyncFileUtilAdapter(new LocalFileUtil())),
+IsolatedFileSystemBackend::IsolatedFileSystemBackend(
+    bool use_for_type_native_local,
+    bool use_for_type_platform_app)
+    : use_for_type_native_local_(use_for_type_native_local),
+      use_for_type_platform_app_(use_for_type_platform_app),
+      isolated_file_util_(new AsyncFileUtilAdapter(new LocalFileUtil())),
       dragged_file_util_(new AsyncFileUtilAdapter(new DraggedFileUtil())),
       transient_file_util_(new AsyncFileUtilAdapter(new TransientFileUtil())) {
 }
@@ -44,11 +48,10 @@ bool IsolatedFileSystemBackend::CanHandleType(FileSystemType type) const {
     case kFileSystemTypeDragged:
     case kFileSystemTypeForTransientFile:
       return true;
-#if !defined(OS_CHROMEOS)
     case kFileSystemTypeNativeLocal:
+      return use_for_type_native_local_;
     case kFileSystemTypeNativeForPlatformApp:
-      return true;
-#endif
+      return use_for_type_platform_app_;
     default:
       return false;
   }
diff --git a/storage/browser/fileapi/isolated_file_system_backend.h b/storage/browser/fileapi/isolated_file_system_backend.h
index 2c12379..bd13db4 100644
--- a/storage/browser/fileapi/isolated_file_system_backend.h
+++ b/storage/browser/fileapi/isolated_file_system_backend.h
@@ -15,7 +15,8 @@ class AsyncFileUtilAdapter;
 
 class IsolatedFileSystemBackend : public FileSystemBackend {
  public:
-  IsolatedFileSystemBackend();
+  IsolatedFileSystemBackend(bool use_for_type_native_local,
+                            bool use_for_type_platform_app);
   ~IsolatedFileSystemBackend() override;
 
   // FileSystemBackend implementation.
@@ -55,6 +56,14 @@ class IsolatedFileSystemBackend : public FileSystemBackend {
       FileSystemType type) const override;
 
  private:
+  // Whether this object should handle native local filesystem types. Some
+  // platforms (e.g. Chrome OS) may provide a different FileSystemBackend to
+  // handle those types.
+  const bool use_for_type_native_local_;
+
+  // As above but for platform webapps.
+  const bool use_for_type_platform_app_;
+
   scoped_ptr<AsyncFileUtilAdapter> isolated_file_util_;
   scoped_ptr<AsyncFileUtilAdapter> dragged_file_util_;
   scoped_ptr<AsyncFileUtilAdapter> transient_file_util_;