Media Galleries: Add a dropPermissionForMediaFileSystem() API.

chrome/browser/extensions/api/media_galleries/media_galleries_api.h

Index: chrome/browser/extensions/api/media_galleries/media_galleries_api.h
===================================================================
--- chrome/browser/extensions/api/media_galleries/media_galleries_api.h	(revision 261942)
+++ chrome/browser/extensions/api/media_galleries/media_galleries_api.h	(working copy)
@@ -179,6 +179,21 @@
   void GetMediaFileSystemsForExtension(const MediaFileSystemsCallback& cb);
 };
 
+class MediaGalleriesForgetMediaFileSystemFunction
+    : public ChromeAsyncExtensionFunction {
+ public:
+  DECLARE_EXTENSION_FUNCTION("mediaGalleries.forgetMediaFileSystem",
+                             MEDIAGALLERIES_FORGETMEDIAFILESYSTEM)
+
+ protected:
+  virtual ~MediaGalleriesForgetMediaFileSystemFunction();
+  virtual bool RunImpl() OVERRIDE;
+
+ private:
+  // Bottom half for RunImpl, invoked after the preferences is initialized.
+  void OnPreferencesInit(MediaGalleryPrefId pref_id);
+};
+
 class MediaGalleriesStartMediaScanFunction
     : public ChromeAsyncExtensionFunction {
  public: