Plumb thru that we cache the front buffer.

Plumb thru that we cache the front buffer.

This allows us to drop the root layer textures and save on VRAM (10 MB on a 30" display).

WebKit side patch: https://bugs.webkit.org/show_bug.cgi?id=72956

BUG=none
TEST='cat /proc/meminfo | grep Shmem' on Intel graphics and use_aura=1 attached to 30" display

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=111532

[jonathan.backer, 2011-11-22 18:21:31]

On 2011/11/22 15:03:02, jonathan.backer wrote:

Did some testing. Dropping the root layer tiles can cost us 150ms on image heavy
pages. Here's how I did the testing:

- used a GPU accelerated smooth scrolling demo with/without dropping root layer
tiles
- rapidly switched tabs
- used chrome://tracing to examine the difference between OnSurfaceSetVisible
and SwapBuffers in the GPU process for the accelerated page

The time gap between SetVisible(true) and SwapBuffers takes 200ms when we drop
root tiles and 50ms when we don't. This is fairly noticeable.

To be fair, we're measuring worst case:
- low end hardware (integrated Intel graphics --- stumpy)
- the tiles are images which are expensive to generate
- with the scrolling test, all the tiles are relevant and need to be regenerated
(with other animations and/or less longer gaps b/w tab switch, probably less
root tiles could be used) 

I think this is a reasonable trade-off.

[apatrick_chromium, 2011-11-23 01:48:35]

lgtm