Move Extension into extensions namespace

chrome/browser/extensions/extension_icon_manager.h

Index: chrome/browser/extensions/extension_icon_manager.h
diff --git a/chrome/browser/extensions/extension_icon_manager.h b/chrome/browser/extensions/extension_icon_manager.h
index 4596d1251fd047d3d2e84fa0e2d8c52f77c9ea5b..d7863dbf38910870a11e7dd90a72ea10640494e1 100644
--- a/chrome/browser/extensions/extension_icon_manager.h
+++ b/chrome/browser/extensions/extension_icon_manager.h
@@ -15,7 +15,9 @@
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/gfx/insets.h"
 
+namespace extensions {
 class Extension;
+}
 
 class ExtensionIconManager : public ImageLoadingTracker::Observer {
  public:
@@ -23,7 +25,7 @@ class ExtensionIconManager : public ImageLoadingTracker::Observer {
   virtual ~ExtensionIconManager();
 
   // Start loading the icon for the given extension.
-  void LoadIcon(const Extension* extension);
+  void LoadIcon(const extensions::Extension* extension);
 
   // This returns a bitmap of width/height kFaviconSize, loaded either from an
   // entry specified in the extension's 'icon' section of the manifest, or a