add getTextureHandle to SkSurface

include/core/SkSurface.h

Index: include/core/SkSurface.h
diff --git a/include/core/SkSurface.h b/include/core/SkSurface.h
index de84766647d993618c814e75a6bc216edd8e2e62..7815f68efb950822c15b01160e0f2562d0ac489e 100644
--- a/include/core/SkSurface.h
+++ b/include/core/SkSurface.h
@@ -140,10 +140,21 @@ public:
     /**
      *  Call this if the contents are about to change. This will (lazily) force a new
      *  value to be returned from generationID() when it is called next.
+     *
+     *  CAN WE DEPRECATE THIS?

[Justin Novosad, 2015/06/26 21:33:14]

No we can't. This API drives an important optimization: it allows us to skip the
'copy' part of copy-on-write when we know the new content will overwrite the
surface's prior contents. It is a piece of magic in SkDeferredCanvas that has an
important impact on performance.

[reed1, 2015/06/27 17:56:11]

Lets discuss as part of DeferredCanvas discussion

      */
     void notifyContentWillChange(ContentChangeMode mode);
 
     /**
+     *  Retrieves the backend API handle of the texture used by this surface, or 0 if the surface
+     *  is not backed by a GPU texture.
+     *
+     *  If flushPendingWrites then the GrContext will issue to the backend API any deferred

[bsalomon, 2015/06/26 21:15:22]

comment looks incorrect

[reed1, 2015/06/26 21:21:13]

Doh

+     *  read operations on the texture before returning.
+     */
+    GrBackendObject getTextureHandle(ContentChangeMode);

[f(malita), 2015/06/26 21:39:38]

Can you also document the lifetime & ownership for this texture/handle?

[reed1, 2015/06/27 17:56:11]

Done.

+
+    /**
      *  Return a canvas that will draw into this surface. This will always
      *  return the same canvas for a given surface, and is manged/owned by the
      *  surface. It should not be used when its parent surface has gone out of