2 files changed, 37 insertions, 4 deletions

diff --git a/chrome/test/test_file_util.cc b/chrome/test/test_file_util.cc
index 633fdc9..5bb55cc 100644
--- a/chrome/test/test_file_util.cc
+++ b/chrome/test/test_file_util.cc
@@ -12,6 +12,34 @@
 
 namespace file_util {
 
+bool EvictFileFromSystemCache(const wchar_t* file) {
+  // Request exclusive access to the file and overwrite it with no buffering.
+  win_util::ScopedHandle hfile(
+      CreateFile(file, GENERIC_READ | GENERIC_WRITE, 0, NULL,
+                 OPEN_EXISTING, FILE_FLAG_NO_BUFFERING,
+                 NULL));
+  if (!hfile)
+    return false;
+
+  // Execute in chunks. It could be optimized. We want to do few of these since
+  // these opterations will be slow without the cache.
+  char buffer[4096];
+  int total_bytes = 0;
+  DWORD bytes_read;
+  for (;;) {
+    bytes_read = 0;
+    ReadFile(hfile, buffer, sizeof(buffer), &bytes_read, NULL);
+    if (bytes_read == 0)
+      break;
+
+    SetFilePointer(hfile, total_bytes, 0, FILE_BEGIN);
+    if (!WriteFile(hfile, buffer, bytes_read, &bytes_read, NULL))
+      return false;
+    total_bytes += bytes_read;
+  }
+  return true;
+}
+
 // Like CopyFileNoCache but recursively copies all files and subdirectories
 // in the given input directory to the output directory.
 bool CopyRecursiveDirNoCache(const std::wstring& source_dir,
@@ -60,7 +88,7 @@ bool CopyRecursiveDirNoCache(const std::wstring& source_dir,
       // files that are in the repository, and they will have read-only set.
       // This will prevent us from evicting from the cache, but these don't
       // matter anyway.
-      file_util::EvictFileFromSystemCache(cur_dest_path.c_str());
+      EvictFileFromSystemCache(cur_dest_path.c_str());
     }
   } while (FindNextFile(fh, &fd));
 
diff --git a/chrome/test/test_file_util.h b/chrome/test/test_file_util.h
index bf415a1..dd4e34f 100644
--- a/chrome/test/test_file_util.h
+++ b/chrome/test/test_file_util.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef CHROME_TEST_TEST_FILE_UTIL_H_
-#define CHROME_TEST_TEST_FILE_UTIL_H_
+#ifndef CHROME_TEST_TEST_FILE_UTIL_H__
+#define CHROME_TEST_TEST_FILE_UTIL_H__
 
 // File utility functions used only by tests.
 
@@ -11,6 +11,11 @@
 
 namespace file_util {
 
+// Clear a specific file from the system cache using a neat trick. After this
+// call, trying to access this file will result in a cold load from the hard
+// drive.
+bool EvictFileFromSystemCache(const wchar_t* file);
+
 // Like CopyFileNoCache but recursively copies all files and subdirectories
 // in the given input directory to the output directory. Any files in the
 // destination that already exist will be overwritten.
@@ -22,5 +27,5 @@ bool CopyRecursiveDirNoCache(const std::wstring& source_dir,
 
 }  // namespace file_util
 
-#endif  // CHROME_TEST_TEST_FILE_UTIL_H_
+#endif  // CHROME_TEST_TEST_FILE_UTIL_H__