Fix CC*Renderer and CC*LayerImpl to compile with Clang

cc/CCIOSurfaceLayerImpl.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CCIOSurfaceLayerImpl_h
 #define CCIOSurfaceLayerImpl_h
 
 #include "CCLayerImpl.h"
 #include "IntSize.h"
 
@@ skipping 12 matching lines @@
     virtual void appendQuads(CCQuadSink&, CCAppendQuadsData&) OVERRIDE;
 
     virtual void willDraw(CCResourceProvider*) OVERRIDE;
     virtual void didLoseContext() OVERRIDE;
 
     virtual void dumpLayerProperties(std::string*, int indent) const OVERRIDE;
 
 private:
     explicit CCIOSurfaceLayerImpl(int);
 
-    virtual const char* layerTypeAsString() const OVERRIDE { return "IOSurfaceLayer"; }
+    virtual const char* layerTypeAsString() const OVERRIDE;
 
     unsigned m_ioSurfaceId;
     IntSize m_ioSurfaceSize;
     bool m_ioSurfaceChanged;
     unsigned m_ioSurfaceTextureId;
 };
 
 }
 
 #endif // CCIOSurfaceLayerImpl_h