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

src/image/SkImage_Gpu.cpp

Index: src/image/SkImage_Gpu.cpp
diff --git a/src/image/SkImage_Gpu.cpp b/src/image/SkImage_Gpu.cpp
index 04939e36f16e191af29c5583aac746e48499cefc..c502fc0092536ddbb971b40a76cf1aa33d6980cb 100644
--- a/src/image/SkImage_Gpu.cpp
+++ b/src/image/SkImage_Gpu.cpp
@@ -326,7 +326,8 @@ GrTexture* GrDeepCopyTexture(GrTexture* src, bool budgeted) {
 
     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;
 }