Cleanup: Remove forward declarations in various chrome/browser directories.

chrome/browser/history/history.h

Index: chrome/browser/history/history.h
===================================================================
--- chrome/browser/history/history.h	(revision 110049)
+++ chrome/browser/history/history.h	(working copy)
@@ -32,28 +32,15 @@
 class GURL;
 class HistoryURLProvider;
 struct HistoryURLProviderParams;
-class InMemoryURLDatabase;
-class MainPagesRequest;
 class PageUsageData;
 class PageUsageRequest;
 class Profile;
-class SkBitmap;
-struct ThumbnailScore;
 
 namespace base {
 class Thread;
 class Time;
 }
 
-namespace browser_sync {
-class HistoryModelWorker;
-class TypedUrlDataTypeController;
-}
-
-namespace gfx {
-class Image;
-}
-
 namespace history {
 class InMemoryHistoryBackend;
 class InMemoryURLIndex;