GrContext::copyTexture->GrContext::copySurface.

Add a flush writes pixel ops flag.

Add an explicit flush writes for GrSurface.

BUG=skia:2977

Committed: https://skia.googlesource.com/skia/+/cf99b00980b6c9c557e71abf1a7c9f9b21217262

Review URL: https://codereview.chromium.org/622663002
diff --git a/samplecode/SampleApp.cpp b/samplecode/SampleApp.cpp
index c190527..e8146f0 100644
--- a/samplecode/SampleApp.cpp
+++ b/samplecode/SampleApp.cpp
@@ -298,10 +298,8 @@
                                              SkImageInfo2GrPixelConfig(bm.colorType(),
                                                                        bm.alphaType()),
                                              bm.getPixels(),
-                                             bm.rowBytes());
-
-                // extra flush call, until Brian can figure out what's going on.
-                fCurContext->flush();
+                                             bm.rowBytes(),
+                                             GrContext::kFlushWrites_PixelOp);
             }
         }
 #endif