Reland again "Decode GIF image frames on demand".

Reland again "Decode GIF image frames on demand".

Change over https://codereview.chromium.org/16260002 (r151564):
- Fix ImageFrame operator =.
- Set requiredPreviousFrameIndex to notFound and premultiplyAlpha to
  m_premultiplyAlpha after the ImageFrame is assigned from PNGImageDecoder
  decoding result.
- Remove ASSERT(m_decodedSize == 0 || frameCount > 1) (which caused bug 246118).
  We could preserve the ASSERT by not clearing m_frames if frameCount == 1 in
  BitmapImage::destroyDecodedData(), but I think we'd better let the decoder
  control which frames to clear. If the frame is not actually cleared, recaching
  the frame is cheap.

Change over https://codereview.chromium.org/15350006 (r151560):
Workaround const_reverse_iterator issue of Android compiler.

Previously GIFImageDecoder::frameBufferAtIndex() decodes all frames from
the last decoded frame to the requested frame. This causes delays when
skipping to specific frames.

With this change, GIFImageDecoder decodes only necessary frames based on
previous frames' disposal methods. Added ImageDecoder::findRequiredPreviousFrame()
to find the required previous frame based on the disposal methods.

Also changed the behavior of GIFImageDecoder::clearFrameBufferCache() (moved to
ImageDecoder because it can be shared between multi-frame decoders) because
the original semantics no longer apply with on-demand frame decoding.
Instead of clearing before the given frame, now clear from the whole frame buffer
cache, preserving the frames that are likely to be used soon.

BUG=238242, 246118
TEST=ImageDecoderTest.requiredPreviousFrameIndex*, ImageDecoderTest.clearCacheExceptFrame*, GIFImageDecoderTest.updateRequiredPreviousFrameAfterFirstDecode, GIFImageDecoderTest.randomFrameDecode, GIFImageDecoderTest.randomDecodeAfterClearFrameBufferCache, GIFImageDecoderTest.resumePartialDecodeAfterClearFrameBufferCache,ICODecoderTest.Decode(in content_unittests).
R=pkasting@chromium.org
TBR=abarth@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=151702

[Peter Kasting, 2013-06-03 18:39:10]

LGTM

https://codereview.chromium.org/15969015/diff/1026/Source/core/platform/image...
File Source/core/platform/image-decoders/ico/ICOImageDecoder.cpp (right):

https://codereview.chromium.org/15969015/diff/1026/Source/core/platform/image...
Source/core/platform/image-decoders/ico/ICOImageDecoder.cpp:240:
m_frameBufferCache[index].setRequiredPreviousFrameIndex(notFound);
Do you need to call setPremultiplyAlpha here as in frameCount() or is that
handled by the PNG decoder?

[Xianzhu, 2013-06-03 18:44:43]

https://codereview.chromium.org/15969015/diff/1026/Source/core/platform/image...
File Source/core/platform/image-decoders/ico/ICOImageDecoder.cpp (right):

https://codereview.chromium.org/15969015/diff/1026/Source/core/platform/image...
Source/core/platform/image-decoders/ico/ICOImageDecoder.cpp:240:
m_frameBufferCache[index].setRequiredPreviousFrameIndex(notFound);
On 2013/06/03 18:39:10, Peter Kasting wrote:
> Do you need to call setPremultiplyAlpha here as in frameCount() or is that
> handled by the PNG decoder?

Yes, we need it. Done.

[commit-bot: I haz the power, 2013-06-03 18:45:04]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/15969015/13001

[commit-bot: I haz the power, 2013-06-03 23:42:22]

Commit queue rejected this change because the description was changed
between the time the change entered the commit queue and the time it
was ready to commit. You can safely check the commit box again.

[commit-bot: I haz the power, 2013-06-03 23:44:28]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/15969015/13001

[commit-bot: I haz the power, 2013-06-03 23:53:12]

Change committed as 151702

[urvang (Google), 2013-06-06 18:33:50]

Noticed this when applying similar changes to my WebP animation patch.

https://chromiumcodereview.appspot.com/15969015/diff/13001/Source/core/platfo...
File Source/core/platform/image-decoders/gif/GIFImageDecoderTest.cpp (right):

https://chromiumcodereview.appspot.com/15969015/diff/13001/Source/core/platfo...
Source/core/platform/image-decoders/gif/GIFImageDecoderTest.cpp:410:
OwnPtr<GIFImageDecoder> decoder = createDecoder();
Need to do "decoder->setData()" after this.

https://chromiumcodereview.appspot.com/15969015/diff/13001/Source/core/platfo...
Source/core/platform/image-decoders/gif/GIFImageDecoderTest.cpp:427:
testRandomFrameDecode("/Source/WebKit/chromium/tests/data/radient.gif");
All these calls should be "testRandomDecodeAfterClearFrameBufferCache()"
instead!!