Move prepareForExternalIO implementation from GrContext to GrDrawingManager

src/gpu/GrDrawingManager.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrDrawingManager_DEFINED
 #define GrDrawingManager_DEFINED
 
@@ skipping 42 matching lines @@
     void flushIfNecessary() {
         if (fContext->getResourceCache()->requestsFlush()) {
             this->internalFlush(GrResourceCache::kCacheRequested);
         } else if (fIsImmediateMode) {
             this->internalFlush(GrResourceCache::kImmediateMode);
         }
     }
 
     static bool ProgramUnitTest(GrContext* context, int maxStages);
 
+    void prepareSurfaceForExternalIO(GrSurface*);
+
 private:
     GrDrawingManager(GrContext* context, const GrDrawTarget::Options& optionsForDrawTargets,
                      bool isImmediateMode, GrSingleOwner* singleOwner)
         : fContext(context)
         , fOptionsForDrawTargets(optionsForDrawTargets)
         , fSingleOwner(singleOwner)
         , fAbandoned(false)
         , fAtlasTextContext(nullptr)
         , fPathRendererChain(nullptr)
         , fSoftwarePathRenderer(nullptr)
@@ skipping 27 matching lines @@
     GrPathRendererChain*              fPathRendererChain;
     GrSoftwarePathRenderer*           fSoftwarePathRenderer;
 
     GrBatchFlushState                 fFlushState;
     bool                              fFlushing;
 
     bool                              fIsImmediateMode;
 };
 
 #endif