Make a single GrSingleOwner in GrContext

src/gpu/GrDrawingManager.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrDrawContext.h"
 #include "GrDrawingManager.h"
 #include "GrDrawTarget.h"
@@ skipping 184 matching lines @@
 
     return pr;
 }
 
 GrDrawContext* GrDrawingManager::drawContext(GrRenderTarget* rt,
                                              const SkSurfaceProps* surfaceProps) {
     if (this->abandoned()) {
         return nullptr;
     }
 
-    return new GrDrawContext(this, rt, surfaceProps);
+    return new GrDrawContext(this, rt, surfaceProps, fSingleOwner);
 }