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

include/gpu/GrDrawContext.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 GrDrawContext_DEFINED
 #define GrDrawContext_DEFINED
 
@@ skipping 29 matching lines @@
 struct SkRSXform;
 class SkTextBlob;
 
 /*
  * A helper object to orchestrate draws
  */
 class SK_API GrDrawContext : public SkRefCnt {
 public:
     ~GrDrawContext() override;
 
-    void copySurface(GrSurface* src, const SkIRect& srcRect, const SkIPoint& dstPoint);
+    bool copySurface(GrSurface* src, const SkIRect& srcRect, const SkIPoint& dstPoint);
 
     // TODO: it is odd that we need both the SkPaint in the following 3 methods.
     // We should extract the text parameters from SkPaint and pass them separately
     // akin to GrStrokeInfo (GrTextInfo?)
     void drawText(const GrClip&,  const GrPaint&, const SkPaint&,
                   const SkMatrix& viewMatrix, const char text[], size_t byteLength,
                   SkScalar x, SkScalar y, const SkIRect& clipBounds);
     void drawPosText(const GrClip&, const GrPaint&, const SkPaint&,
                      const SkMatrix& viewMatrix, const char text[], size_t byteLength,
                      const SkScalar pos[], int scalarsPerPosition,
@@ skipping 253 matching lines @@
     GrContext*        fContext;
 
     SkSurfaceProps    fSurfaceProps;
     GrAuditTrail*     fAuditTrail;
 
     // In debug builds we guard against improper thread handling
     SkDEBUGCODE(mutable GrSingleOwner* fSingleOwner;)
 };
 
 #endif