add getTextureHandle to SkSurface

BUG=485243

Review URL: https://codereview.chromium.org/1210303003
diff --git a/src/image/SkSurface.cpp b/src/image/SkSurface.cpp
index a999973..34035a3 100644
--- a/src/image/SkSurface.cpp
+++ b/src/image/SkSurface.cpp
@@ -175,6 +175,10 @@
     return this->getCanvas()->readPixels(dstInfo, dstPixels, dstRowBytes, srcX, srcY);
 }
 
+GrBackendObject SkSurface::getTextureHandle(TextureHandleAccess access) {
+    return asSB(this)->onGetTextureHandle(access);
+}
+
 //////////////////////////////////////////////////////////////////////////////////////
 
 #if !SK_SUPPORT_GPU