Add hooks for GL_EXT_debug_marker in gpu

src/gpu/gl/GrGpuGL.h

Index: src/gpu/gl/GrGpuGL.h
diff --git a/src/gpu/gl/GrGpuGL.h b/src/gpu/gl/GrGpuGL.h
index edd58c44bc8675290873d6942d5bd30ac0699339..05802550af85d970a944bfe0ac5ef442f508e4eb 100644
--- a/src/gpu/gl/GrGpuGL.h
+++ b/src/gpu/gl/GrGpuGL.h
@@ -162,6 +162,12 @@ private:
                                   bool insideClip) SK_OVERRIDE;
     virtual bool flushGraphicsState(DrawType, const GrDeviceCoordTexture* dstCopy) SK_OVERRIDE;
 
+    // GrDrawTarget ovverides
+    virtual void onInstantGpuTraceEvent(const char* marker) SK_OVERRIDE;
+    virtual void onPushGpuTraceEvent(const char* marker) SK_OVERRIDE;
+    virtual void onPopGpuTraceEvent() SK_OVERRIDE;
+
+
     // binds texture unit in GL
     void setTextureUnit(int unitIdx);