content: Cleanup class/struct forward declarations

content/browser/compositor/browser_compositor_output_surface.h

Index: content/browser/compositor/browser_compositor_output_surface.h
diff --git a/content/browser/compositor/browser_compositor_output_surface.h b/content/browser/compositor/browser_compositor_output_surface.h
index 7084ec1c22022b6cf108aa6df3ed4a55cefe61b4..e049e4d1bb5ffdc57dd60b7985f4e87c97493628 100644
--- a/content/browser/compositor/browser_compositor_output_surface.h
+++ b/content/browser/compositor/browser_compositor_output_surface.h
@@ -25,14 +25,8 @@ namespace gfx {
 enum class SwapResult;
 }
 
-namespace gpu {
-struct GpuProcessHostedCALayerTreeParamsMac;
-}
-
 namespace content {
-class ContextProviderCommandBuffer;
 class ReflectorImpl;
-class WebGraphicsContext3DCommandBufferImpl;
 
 class CONTENT_EXPORT BrowserCompositorOutputSurface
     : public cc::OutputSurface {