Move Extension into extensions namespace

chrome/browser/extensions/extension_tabs_module.h

Index: chrome/browser/extensions/extension_tabs_module.h
diff --git a/chrome/browser/extensions/extension_tabs_module.h b/chrome/browser/extensions/extension_tabs_module.h
index 085b7437733c31195c734e4eb9918c8069110abf..4a1c52f21d094940dc9b0c14fcd21a69beeeb6f4 100644
--- a/chrome/browser/extensions/extension_tabs_module.h
+++ b/chrome/browser/extensions/extension_tabs_module.h
@@ -17,19 +17,21 @@
 #include "googleurl/src/gurl.h"
 
 class BackingStore;
-class Extension;
 class GURL;
 class SkBitmap;
 class TabContentsWrapper;
+
 namespace base {
 class DictionaryValue;
-}  // namespace base
+}
+
 namespace content {
 class WebContents;
-}  // namespace content
+}
+
 namespace skia {
 class PlatformCanvas;
-}  // namespace skia
+}
 
 // Windows
 class GetWindowFunction : public SyncExtensionFunction {