Add wrapBackendTextureAsRenderTarget API

src/image/SkSurface_Base.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkSurface_Base_DEFINED
 #define SkSurface_Base_DEFINED
 
@@ skipping 56 matching lines @@
      *  being shared with the cachedImage.
      */
     virtual void onCopyOnWrite(ContentChangeMode) = 0;
 
     /**
      *  Signal the surface to remind its backing store that it's mutable again.
      *  Called only when we _didn't_ copy-on-write; we assume the copies start mutable.
      */
     virtual void onRestoreBackingMutability() {}
 
+    /**
+     * Issue any pending surface IO to the current backend 3D API and resolve any surface MSAA.
+     */
+    virtual void onPrepareForExternalIO() {}
+
     inline SkCanvas* getCachedCanvas();
     inline SkImage* getCachedImage(Budgeted);
 
     bool hasCachedImage() const { return fCachedImage != nullptr; }
 
     // called by SkSurface to compute a new genID
     uint32_t newGenerationID();
 
 private:
     SkCanvas*   fCachedCanvas;
@@ skipping 23 matching lines @@
 
 SkImage* SkSurface_Base::getCachedImage(Budgeted budgeted) {
     if (nullptr == fCachedImage) {
         fCachedImage = this->onNewImageSnapshot(budgeted);
         SkASSERT(!fCachedCanvas || fCachedCanvas->getSurfaceBase() == this);
     }
     return fCachedImage;
 }
 
 #endif