Add rendering fast path for when playing a display list canvas at 1:1 scale

Add rendering fast path for when playing a display list canvas at 1:1 scale

This patch modifies GraphicsContext::drawPicture to make it
avoid the use of image filters for presenting canvas
contents, and just use a plain save layer when drawing
contents at 1:1 pixel scale.

BUG=386601
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=183836

[Justin Novosad, 2014-10-16 15:30:35]

junov@chromium.org changed reviewers:
+ senorblanco@chromium.org

[Justin Novosad, 2014-10-16 15:30:36]

PTAL

[Stephen White, 2014-10-16 17:38:00]

https://codereview.chromium.org/662673002/diff/1/Source/platform/graphics/Gra...
File Source/platform/graphics/GraphicsContext.cpp (right):

https://codereview.chromium.org/662673002/diff/1/Source/platform/graphics/Gra...
Source/platform/graphics/GraphicsContext.cpp:1134: return x > 0.999999 && x <
1.000001;
Could you put this in a constant at the start of the file (e.g.,
kPictureScaleEpsilon), and use fabsf(x - 1.0f) < kPictureScaleEpsilon? Would
that work?

https://codereview.chromium.org/662673002/diff/1/Source/platform/graphics/Gra...
Source/platform/graphics/GraphicsContext.cpp:1152: if
(pictureScaleIsApproximatelyOne(scaleX * m_deviceScaleFactor) &&
pictureScaleIsApproximatelyOne(scaleY * m_deviceScaleFactor)) {
I'm not certain, but I think that using the device scale factor at record time
may be problematic for devices which have both hiDPI and loDPI displays (e.g., a
retina MBP connected to a loDPI display), since we don't know which device will
be used at playback.

Anyway, not enough to block this change, but something to watch out for.

[Justin Novosad, 2014-10-16 18:01:11]

new patch

[Stephen White, 2014-10-16 18:49:39]

https://codereview.chromium.org/662673002/diff/20001/Source/platform/graphics...
File Source/platform/graphics/GraphicsContext.cpp (right):

https://codereview.chromium.org/662673002/diff/20001/Source/platform/graphics...
Source/platform/graphics/GraphicsContext.cpp:68: const float
kPictureScaleEpsilon = 0.000001;
Looks like I just made you do a skia-ism. :( Looks like this should be
cPictureScaleEpsilon, or nothing at all (pictureScaleEpsilon). Sorry!

[Justin Novosad, 2014-10-16 18:50:49]

new patch

[Stephen White, 2014-10-16 18:56:12]

LGTM

[Justin Novosad, 2014-10-16 18:58:44]

The CQ bit was checked by junov@chromium.org

[commit-bot: I haz the power, 2014-10-16 18:59:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/662673002/40001

[commit-bot: I haz the power, 2014-10-16 21:01:38]

Committed patchset #3 (id:40001) as 183836