Add wrapBackendTextureAsRenderTarget API

src/image/SkSurface_Base.h

Index: src/image/SkSurface_Base.h
diff --git a/src/image/SkSurface_Base.h b/src/image/SkSurface_Base.h
index 7658409ad764eb78cdcb330d5ea13897d986c83f..f4efde441390df0edd400f21ad1058509251fdf5 100644
--- a/src/image/SkSurface_Base.h
+++ b/src/image/SkSurface_Base.h
@@ -74,6 +74,11 @@ public:
      */
     virtual void onRestoreBackingMutability() {}
 
+    /**
+     * Issue any pending surface IO to the current backend 3D API and resolve any surface MSAA.
+     */
+    virtual void onPrepareForExternalIO() {}
+
     inline SkCanvas* getCachedCanvas();
     inline SkImage* getCachedImage(Budgeted);