chrome: Cleanup class/struct forward declarations

chrome/browser/android/offline_pages/prerendering_loader.h

Index: chrome/browser/android/offline_pages/prerendering_loader.h
diff --git a/chrome/browser/android/offline_pages/prerendering_loader.h b/chrome/browser/android/offline_pages/prerendering_loader.h
index 01ec2743b4db53661578b102916fe0119ec45a73..1dee3b90ced64df76f22eb04da3c5f1f180dfd70 100644
--- a/chrome/browser/android/offline_pages/prerendering_loader.h
+++ b/chrome/browser/android/offline_pages/prerendering_loader.h
@@ -17,13 +17,8 @@ class GURL;
 namespace content {
 class BrowserContext;
 class WebContents;
-class SessionStorageNamespace;
 }  // namespace content
 
-namespace gfx {
-class Size;
-}  // namespace gfx
-
 namespace offline_pages {
 
 // A client-side page loader that integrates with the PrerenderManager to do