Add GpuCommandBuffer support.

src/gpu/GrGpu.h

Index: src/gpu/GrGpu.h
diff --git a/src/gpu/GrGpu.h b/src/gpu/GrGpu.h
index 63a56ddd2d42bebd0bf4a38190a2521d0f9652a4..a99ce8f45e4370c042640dbca967ea4ca042004a 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -8,6 +8,7 @@
 #ifndef GrGpu_DEFINED
 #define GrGpu_DEFINED
 
+#include "GrGpuCommandBuffer.h"
 #include "GrPipelineBuilder.h"
 #include "GrProgramDesc.h"
 #include "GrSwizzle.h"
@@ -360,6 +361,14 @@ public:
     // multisample information itself.
     const MultisampleSpecs& getMultisampleSpecs(GrRenderTarget*, const GrStencilSettings&);
 
+    // Creates a GrGpuCommandBuffer in which the GrDrawTarget can send draw commands to instead of
+    // directly to the Gpu object.
+    virtual GrGpuCommandBuffer* createCommandBuffer(const GrRenderTarget& target,
+                                                    GrGpuCommandBuffer::LoadAndStoreOp colorOp,
+                                                    GrColor colorClear,
+                                                    GrGpuCommandBuffer::LoadAndStoreOp stencilOp,
+                                                    GrColor stencilClear) = 0;
+
     // We pass in an array of meshCount GrMesh to the draw. The backend should loop over each
     // GrMesh object and emit a draw for it. Each draw will use the same GrPipeline and
     // GrPrimitiveProcessor. This may fail if the draw would exceed any resource limits (e.g.