Start using GrGpuCommandBuffer in GrDrawTarget.

src/gpu/gl/GrGLGpuCommandBuffer.h

 /*
 * Copyright 2016 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #ifndef GrGLGpuCommandBuffer_DEFINED
 #define GrGLGpuCommandBuffer_DEFINED
 
 #include "GrGpuCommandBuffer.h"
 
-class GrGLGpu;
+#include "GrGLGpu.h"
 
 class GrGLGpuCommandBuffer : public GrGpuCommandBuffer {
+/**
+ * We do not actually buffer up draws or do any work in the this class for GL. Instead commands
+ * are immediately sent to the gpu to execute. Thus all the commands in this class are simply
+ * pass through functions to corresponding calls in the GrGLGpu class.
+ */
 public:
-    GrGLGpuCommandBuffer(GrGLGpu* gpu) /*: fGpu(gpu)*/ {}
+    GrGLGpuCommandBuffer(GrGLGpu* gpu) : fGpu(gpu) {}
 
     virtual ~GrGLGpuCommandBuffer() {}
 
     void end() override {}
 
-    void submit() override {}
+    void discard(GrRenderTarget* rt) override { fGpu->discard(rt); }
 
 private:
-    // commented out to appease clang compiler warning about unused private field
-   // GrGLGpu*                    fGpu;
+    GrGpu* gpu() override { return fGpu; }
+
+    void onSubmit(const SkIRect& bounds) override {}
+
+    void onDraw(const GrPipeline& pipeline,
+                const GrPrimitiveProcessor& primProc,
+                const GrMesh* mesh,
+                int meshCount) override {
+        fGpu->draw(pipeline, primProc, mesh, meshCount);
+    }
+
+    void onClear(GrRenderTarget* rt, const SkIRect& rect, GrColor color) override {
+        fGpu->clear(rect, color, rt);
+    }
+
+    void onClearStencilClip(GrRenderTarget* rt, const SkIRect& rect, bool insideClip) override {
+        fGpu->clearStencilClip(rect, insideClip, rt);
+    }
+
+    GrGLGpu*                    fGpu;
 
     typedef GrGpuCommandBuffer INHERITED;
 };
 
 #endif