Add Gr*Proxy classes

include/gpu/GrRenderTarget.h

Index: include/gpu/GrRenderTarget.h
diff --git a/include/gpu/GrRenderTarget.h b/include/gpu/GrRenderTarget.h
index eb9f142211c9aef75f0e637ab655737dabd57d02..ff75af37e8fe49426db0365b3532a25872446b9a 100644
--- a/include/gpu/GrRenderTarget.h
+++ b/include/gpu/GrRenderTarget.h
@@ -11,6 +11,7 @@
 #include "GrSurface.h"
 #include "SkRect.h"
 
+class GrCaps;
 class GrDrawTarget;
 class GrStencilAttachment;
 class GrRenderTargetPriv;
@@ -155,6 +156,8 @@ public:
     void setLastDrawTarget(GrDrawTarget* dt);
     GrDrawTarget* getLastDrawTarget() { return fLastDrawTarget; }
 
+    static SampleConfig ComputeSampleConfig(const GrCaps& caps, int sampleCnt);
+
 protected:
     GrRenderTarget(GrGpu* gpu, const GrSurfaceDesc& desc,
                    SampleConfig sampleConfig, GrStencilAttachment* stencil = nullptr)