Added CommandBuffer::GetLastError.

gpu/command_buffer/common/command_buffer.h

Index: gpu/command_buffer/common/command_buffer.h
===================================================================
--- gpu/command_buffer/common/command_buffer.h	(revision 119905)
+++ gpu/command_buffer/common/command_buffer.h	(working copy)
@@ -134,6 +134,12 @@
   // call this first.
   virtual void SetContextLostReason(error::ContextLostReason) = 0;
 
+  // TODO(apatrick): this is a temporary optimization while skia is calling
+  // RendererGLContext::MakeCurrent prior to every GL call. It saves returning 6
+  // ints redundantly when only the error is needed for the CommandBufferProxy
+  // implementation.
+  virtual error::Error GetLastError();
+
  private:
   DISALLOW_COPY_AND_ASSIGN(CommandBuffer);
 };