Switch GrTextureToYUVPlanes over to newDrawContext calls

include/gpu/GrContext.h

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrContext_DEFINED
 #define GrContext_DEFINED
 
@@ skipping 178 matching lines @@
      * @param  rt           the render target receiving the draws
      * @param  surfaceProps the surface properties (mainly defines text drawing)
      *
      * @return a draw context
      */
     sk_sp<GrDrawContext> drawContext(sk_sp<GrRenderTarget> rt, const SkSurfaceProps* = nullptr);
 
     /**
      * Create both a GrRenderTarget and a matching GrDrawContext to wrap it.
      * The created GrRenderTarget will always be budgeted.
+     * We guarantee that "asTexture" will succeed for drawContexts created
+     * via this entry point.
      */
     sk_sp<GrDrawContext> newDrawContext(SkBackingFit fit, 
                                         int width, int height,
                                         GrPixelConfig config,
                                         int sampleCnt = 0,
                                         GrSurfaceOrigin origin = kDefault_GrSurfaceOrigin,
                                         const SkSurfaceProps* surfaceProps = nullptr);
 
     ///////////////////////////////////////////////////////////////////////////
     // Misc.
@@ skipping 287 matching lines @@
     SkAutoTUnref<const GrCaps>  fCaps;
     uint32_t                    fContextUniqueID;
 
     friend class GrContext;
     friend class SkImage;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif