add getTextureHandle to SkSurface

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 30af9761d362c4de4216981df6298cf48405bc9c..2712ba6653e12558ccf3c2df604fcf8b4f5fedee 100644
--- a/src/image/SkSurface_Base.h
+++ b/src/image/SkSurface_Base.h
@@ -18,6 +18,10 @@ public:
     SkSurface_Base(const SkImageInfo&, const SkSurfaceProps*);
     virtual ~SkSurface_Base();
 
+    virtual GrBackendObject onGetTextureHandle(ContentChangeMode) {
+        return 0;
+    }
+
     /**
      *  Allocate a canvas that will draw into this surface. We will cache this
      *  canvas, to return the same object to the caller multiple times. We