Extend SkImageGenerator to support natively generated GrTextures

src/core/SkImageCacherator.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 SkImageCacherator_DEFINED
+#define SkImageCacherator_DEFINED
+
+#include "SkImageGenerator.h"
+
+class GrContext;
+class SkBitmap;
+
+/*
+ *  Internal class to manage caching the output of an ImageGenerator.
+ */
+class SkImageCacherator {
+public:
+    // Takes ownership of the generator
+    SkImageCacherator(SkImageGenerator* gen);
+    ~SkImageCacherator();
+
+    const SkImageInfo& info() const { return fGenerator->getInfo(); }
+    SkImageGenerator* generator() const { return fGenerator; }
+
+    /**
+     *  On success (true), bitmap will point to the pixels for this generator. If this returns
+     *  false, the bitmap will be reset to empty.
+     *
+     *  The cached bitmap is valid until it goes out of scope.
+     */
+    bool lockAsBitmap(SkBitmap*);
+
+    /**
+     *  Returns a ref() on the texture produced by this generator. The caller must call unref()
+     *  when it is done. Will return NULL on failure.
+     *
+     *  The cached texture is valid until it is unref'd.
+     */
+    GrTexture* lockAsTexture(GrContext*, SkImageUsageType);
+
+private:
+    bool tryLockAsBitmap(SkBitmap*);
+    GrTexture* tryLockAsTexture(GrContext*, SkImageUsageType);
+
+    SkImageGenerator* fGenerator;
+};
+
+#endif