4 files changed, 21 insertions, 13 deletions

diff --git a/chrome/common/extensions/extension.cc b/chrome/common/extensions/extension.cc
index 63d0b28..7e60ee4 100644
--- a/chrome/common/extensions/extension.cc
+++ b/chrome/common/extensions/extension.cc
@@ -851,6 +851,8 @@ void Extension::DecodeIcon(Extension* extension,
 void Extension::DecodeIconFromPath(const FilePath& icon_path,
                                    Icons icon_size,
                                    scoped_ptr<SkBitmap>* result) {
+  ExtensionResource::CheckFileAccessFromFileThread();
+
   if (icon_path.empty())
     return;
 
@@ -1492,8 +1494,8 @@ void Extension::SetCachedImage(const ExtensionResource& source,
   DCHECK(source.extension_root() == path());  // The resource must come from
                                               // this extension.
   image_cache_[source.relative_path()] = image;
-
 }
+
 bool Extension::HasCachedImage(const ExtensionResource& source) {
   DCHECK(source.extension_root() == path());  // The resource must come from
                                               // this extension.
diff --git a/chrome/common/extensions/extension.h b/chrome/common/extensions/extension.h
index 7559162..165436a 100644
--- a/chrome/common/extensions/extension.h
+++ b/chrome/common/extensions/extension.h
@@ -187,20 +187,18 @@ class Extension {
   static bool IsPrivilegeIncrease(Extension* old_extension,
                                   Extension* new_extension);
 
-  // *** HITS THE FILESYSTEM. Do not call on UI thread! ***
   // Given an extension and icon size, read it if present and decode it into
-  // result.
-  // NOTE: If you need the icon on the UI thread, please use the
-  // ImageLoadingTracker, which uses the File thread internally to decode.
+  // result. In the browser process, this will DCHECK if not called on the
+  // file thread. To easily load extension images on the UI thread, see
+  // ImageLoadingTracker.
   static void DecodeIcon(Extension* extension,
                          Icons icon_size,
                          scoped_ptr<SkBitmap>* result);
 
-  // *** HITS THE FILESYSTEM. Do not call on UI thread! ***
   // Given an icon_path and icon size, read it if present and decode it into
-  // result.
-  // NOTE: If you need the icon on the UI thread, please use the
-  // ImageLoadingTracker, which uses the File thread internally to decode.
+  // result. In the browser process, this will DCHECK if not called on the
+  // file thread. To easily load extension images on the UI thread, see
+  // ImageLoadingTracker.
   static void DecodeIconFromPath(const FilePath& icon_path,
                                  Icons icon_size,
                                  scoped_ptr<SkBitmap>* result);
diff --git a/chrome/common/extensions/extension_resource.cc b/chrome/common/extensions/extension_resource.cc
index eda2d26..eb5b3626 100644
--- a/chrome/common/extensions/extension_resource.cc
+++ b/chrome/common/extensions/extension_resource.cc
@@ -36,8 +36,7 @@ const FilePath& ExtensionResource::GetFilePathOnAnyThreadHack() const {
 }
 
 const FilePath& ExtensionResource::GetFilePath() const {
-  DCHECK(!check_for_file_thread_  ||
-         ExtensionResource::file_thread_id_ == PlatformThread::CurrentId());
+  ExtensionResource::CheckFileAccessFromFileThread();
   return GetFilePathOnAnyThreadHack();
 }
 
@@ -71,11 +70,16 @@ FilePath ExtensionResource::GetFilePathOnAnyThreadHack(
 // static
 FilePath ExtensionResource::GetFilePath(
     const FilePath& extension_root, const FilePath& relative_path) {
-  DCHECK(!check_for_file_thread_ ||
-         ExtensionResource::file_thread_id_ == PlatformThread::CurrentId());
+  CheckFileAccessFromFileThread();
   return GetFilePathOnAnyThreadHack(extension_root, relative_path);
 }
 
+// static
+void ExtensionResource::CheckFileAccessFromFileThread() {
+  DCHECK(!check_for_file_thread_ ||
+         file_thread_id_ == PlatformThread::CurrentId());
+}
+
 // Unit-testing helpers.
 FilePath::StringType ExtensionResource::NormalizeSeperators(
     FilePath::StringType path) const {
diff --git a/chrome/common/extensions/extension_resource.h b/chrome/common/extensions/extension_resource.h
index 755c959..8856414 100644
--- a/chrome/common/extensions/extension_resource.h
+++ b/chrome/common/extensions/extension_resource.h
@@ -46,6 +46,10 @@ class ExtensionResource {
     check_for_file_thread_ = true;
   }
 
+  // Checks whether we are running on the file thread and DCHECKs if not. Relies
+  // on set_file_thread_id being called first, otherwise, it will not DCHECK.
+  static void CheckFileAccessFromFileThread();
+
   // Getters
   const FilePath& extension_root() const { return extension_root_; }
   const FilePath& relative_path() const { return relative_path_; }