add gm for image->newShader

src/utils/SkImageGeneratorUtils.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkImageGeneratorUtils_DEFINED
+#define SkImageGeneratorUtils_DEFINED
+
+#include "SkImageGenerator.h"
+
+class SkImage;
+
+class SkImageGeneratorUtils {
+public:
+    // Returns a generator of the specified dimensions, but will always fail to return anything
+    static SkImageGenerator* NewEmpty(const SkImageInfo&);
+
+    // If the bitmap is mutable, it will make a copy first
+    static SkImageGenerator* NewFromBitmap(const SkBitmap&);
+
+    // Ref's the provided texture, so it had better be const!
+    static SkImageGenerator* NewFromTexture(GrContext*, GrTexture*);
+
+    static SkImageGenerator* NewFromImage(const SkImage*);
+};
+
+#endif