Add notifyPixelsChanged() to inner loop of BitmapScaleBench.

Adding this call simulates seeing a *different* bitmap every time we scale, which changes the code path (places much heavier load on constructing a new filter). This better emulates the kind of environment most embedders see us in, where they try to cache a scaled bitmap rather than frequently rescaling it.

This change will cause significant regressions in microbenchmark scores.

BUG=skia:2236
R=humper@google.com,reed@google.com,scroggo@google.com

Committed: http://code.google.com/p/skia/source/detail?r=13685

[tomhudson, 2014-03-06 12:20:30]

Ready for argument.

[tomhudson, 2014-03-06 14:55:33]

Since Skia now automatically caches scaled bitmaps, this benchmark wasn't
measuring much of what it was supposed to.

Erasing the input bitmap every time through invalidates the cache and lets us
measure a bit more accurately. Mike, Leon, is there a cheaper bit we could flip
to get the invalidation?

[humper, 2014-03-06 14:58:00]

On 2014/03/06 12:20:30, tomhudson wrote:
> Ready for argument.

It looks like a cheaper way to do what you want (circumvent the image cache to
actually benchmark scaling) would be to call notifyPixelsChanged on the bitmap.

[tomhudson, 2014-03-06 15:46:37]

Greg's right, notifyPixelsChanged() triggers the proper behavior without any
apparent overhead. PTAL?

[reed1, 2014-03-06 15:53:58]

that seems as cheap as I can imagine. Is that effectively what chrome has to do
for animated GIF?

[scroggo, 2014-03-06 15:55:55]

lgtm

[tomhudson, 2014-03-06 16:00:30]

The CQ bit was checked by tomhudson@google.com

[commit-bot: I haz the power, 2014-03-06 16:00:48]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/tomhudson@chromium.org/183763047/20001

[tomhudson, 2014-03-06 16:20:06]

On 2014/03/06 15:53:58, reed1 wrote:
> that seems as cheap as I can imagine. Is that effectively what chrome has to
do
> for animated GIF?

Sorry, didn't see your question, just Leon's signoff. This code has changed
since we forked Blink, but it looks to me like
platform/image-decoders/ImageFrame::notifyBitmapIfPixelsChanged() does so, being
called by any of the decoders in frameBufferAtIndex().

[commit-bot: I haz the power, 2014-03-06 17:16:38]

Change committed as 13685