content: Cleanup class/struct forward declarations

content/browser/renderer_host/render_widget_host_view_aura.h

Index: content/browser/renderer_host/render_widget_host_view_aura.h
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.h b/content/browser/renderer_host/render_widget_host_view_aura.h
index 867a3e5a31a824c02aca72300948b190f3f94c95..e78da6c89b22146e060a8bbe3c7b3d15bf1fc3a5 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.h
+++ b/content/browser/renderer_host/render_widget_host_view_aura.h
@@ -50,30 +50,18 @@ class ScopedTooltipDisabler;
 }
 }
 
-namespace cc {
-class CopyOutputRequest;
-class CopyOutputResult;
-}
-
 namespace gfx {
-class Canvas;
 class Display;
 class Point;
 class Rect;
 }
 
-namespace gpu {
-struct Mailbox;
-}
-
 namespace ui {
-class CompositorLock;
 class InputMethod;
 class LocatedEvent;
 #if defined(OS_WIN)
 class OnScreenKeyboardObserver;
 #endif
-class Texture;
 class TouchSelectionController;
 }
 
@@ -84,7 +72,6 @@ class LegacyRenderWidgetHostHWND;
 
 class OverscrollController;
 class RenderFrameHostImpl;
-class RenderViewHostDelegateView;
 class RenderWidgetHostImpl;
 class RenderWidgetHostView;
 class TouchSelectionControllerClientAura;