Move MessageLoop to base namespace.

content/public/browser/browser_thread.h

Index: content/public/browser/browser_thread.h
diff --git a/content/public/browser/browser_thread.h b/content/public/browser/browser_thread.h
index 9ab20522725a3ce63fc110f8ead0189bd02ca9ef..52c87f4062621ecffe6e973148f4edef5f5f7187 100644
--- a/content/public/browser/browser_thread.h
+++ b/content/public/browser/browser_thread.h
@@ -19,9 +19,8 @@
 #include "base/logging.h"
 #endif  // UNIT_TEST
 
-class MessageLoop;
-
 namespace base {
+class MessageLoop;
 class SequencedWorkerPool;
 class Thread;
 }
@@ -216,7 +215,7 @@ class CONTENT_EXPORT BrowserThread {
   //
   // Ownership remains with the BrowserThread implementation, so you
   // must not delete the pointer.
-  static MessageLoop* UnsafeGetMessageLoopForThread(ID identifier);
+  static base::MessageLoop* UnsafeGetMessageLoopForThread(ID identifier);
 
   // Sets the delegate for the specified BrowserThread.
   //