Add transfer buffer support.

src/gpu/GrGpu.h

Index: src/gpu/GrGpu.h
diff --git a/src/gpu/GrGpu.h b/src/gpu/GrGpu.h
index c5fa61bd99851d9b9e5a58d56d14f5a7c7f7573b..4051e69097d236493b362f0702c2f21dff0efa30 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -31,6 +31,7 @@ class GrRenderTarget;
 class GrStencilAttachment;
 class GrSurface;
 class GrTexture;
+class GrTransferBuffer;
 class GrVertexBuffer;
 class GrVertices;
 
@@ -129,6 +130,17 @@ public:
     GrIndexBuffer* createIndexBuffer(size_t size, bool dynamic);
 
     /**
+     * Creates a transfer buffer.
+     *
+     * @param size      size in bytes of the index buffer
+     * @param toGpu     true if used to transfer from the cpu to the gpu

[bsalomon, 2015/12/02 16:38:31]

Maybe an enum instead of a bool for clarity at the call sites? something like

enum {
kCpuToGpu_TransferType
kGpuToGpu_TransferType
};

[jvanverth1, 2015/12/02 18:05:07]

Done.

+     *                  otherwise to be used to transfer from the gpu to the cpu
+     *
+     * @return The transfer buffer if successful, otherwise nullptr.
+     */
+    GrTransferBuffer* createTransferBuffer(size_t size, bool toGpu);
+    
+    /**
      * Resolves MSAA.
      */
     void resolveRenderTarget(GrRenderTarget* target);
@@ -450,6 +462,7 @@ private:
                                                       GrWrapOwnership) = 0;
     virtual GrVertexBuffer* onCreateVertexBuffer(size_t size, bool dynamic) = 0;
     virtual GrIndexBuffer* onCreateIndexBuffer(size_t size, bool dynamic) = 0;
+    virtual GrTransferBuffer* onCreateTransferBuffer(size_t size, bool toGpu) = 0;
 
     // overridden by backend-specific derived class to perform the clear.
     virtual void onClear(GrRenderTarget*, const SkIRect& rect, GrColor color) = 0;