Add support for multiple frames in SkCodec

src/codec/SkCodecAnimation.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkCodecAnimation_DEFINED
+#define SkCodecAnimation_DEFINED
+
+#include "SkRect.h"
+
+class SkCodecAnimation {
+public:
+    /**
+     *  This specifies how the next frame is based on this frame.
+     *
+     *  Names are based on the GIF 89a spec.
+     *
+     *  The numbers correspond to values in a GIF.
+     */
+    enum DisposalMethod {
+        /**
+         *  The next frame should be drawn on top of this one.
+         *
+         *  In a GIF, a value of 0 (not specified) is also treated as Keep.
+         */
+        Keep_DisposalMethod             = 1,
+
+        /**
+         *  Similar to Keep, except the area inside this frame's rectangle
+         *  should be cleared to the BackGround color (transparent) before
+         *  drawing the next frame.
+         */
+        RestoreBGColor_DisposalMethod   = 2,
+
+        /**
+         *  The next frame should be drawn on top of the previous frame - i.e.
+         *  disregarding this one.
+         *
+         *  In a GIF, a value of 4 is treated as RestorePrevious.

[msarett, 2016/09/22 22:54:34]

nit: also?

[scroggo, 2016/09/23 15:53:15]

Haha, yes, that will be more clear.

+         */
+        RestorePrevious_DisposalMethod  = 3,
+    };
+
+    struct FrameInfo {
+        DisposalMethod fDisposalMethod;
+
+        // The frame that this frame is drawn on top of, or
+        // SkCodec::kIndependentFrame.
+        size_t fRequiredFrame;
+
+        // The subset of the bounds that this frame describes.
+        SkIRect fFrameRect;
+
+        // How many 1/100 seconds to show this frame.
+        size_t fDuration;
+    };
+private:
+    SkCodecAnimation();
+};
+#endif // SkCodecAnimation_DEFINED