Make copySurface work for texture dsts, return a bool, & add unit test.

src/image/SkImage_Gpu.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrCaps.h"
 #include "GrContext.h"
 #include "GrDrawContext.h"
@@ skipping 308 matching lines @@
     GrContext* ctx = src->getContext();
 
     GrSurfaceDesc desc = src->desc();
     GrTexture* dst = ctx->textureProvider()->createTexture(desc, budgeted, nullptr, 0);
     if (!dst) {
         return nullptr;
     }
 
     const SkIRect srcR = SkIRect::MakeWH(desc.fWidth, desc.fHeight);
     const SkIPoint dstP = SkIPoint::Make(0, 0);
-    ctx->copySurface(dst, src, srcR, dstP, GrContext::kFlushWrites_PixelOp);
+    ctx->copySurface(dst, src, srcR, dstP);
+    ctx->flushSurfaceWrites(dst);
     return dst;
 }