Move prepareForExternalIO from GrRenderTarget to GrDrawContext

include/gpu/GrDrawContext.h

Index: include/gpu/GrDrawContext.h
diff --git a/include/gpu/GrDrawContext.h b/include/gpu/GrDrawContext.h
index 3cc57b5365a64fd43e739a6f0887dda498dd7288..01f4ac963b47f31c96e09b6a9115e8b21e1f4091 100644
--- a/include/gpu/GrDrawContext.h
+++ b/include/gpu/GrDrawContext.h
@@ -253,6 +253,12 @@ public:
                        const SkIRect& center,
                        const SkRect& dst);
 
+    /**
+     * After this returns any pending surface IO will be issued to the backend 3D API and
+     * if the surface has MSAA it will be resolved.
+     */
+    void prepareForExternalIO();
+
     bool isStencilBufferMultisampled() const {
         return fRenderTarget->isStencilBufferMultisampled();
     }