cc: Reduce number of partial resource updates.

cc: Disable partial resource updates on Android.
    
This makes partialTextureUpdatesMax constant 0 when building for OS_ANDROID.
    
BUG=156945
TEST=manual


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=166347

[nduca, 2012-11-05 06:52:38]

Why? Benchmarks that back up the win? No changes without benchmarks. If the
benchmark doesn't exist, write it.

[reveman, 2012-11-05 18:14:37]

On 2012/11/05 06:52:38, nduca wrote:
> Why? Benchmarks that back up the win? No changes without benchmarks. If the
> benchmark doesn't exist, write it.

I don't mind delaying the change from 12 to 4 until our benchmarks catch up.
Android has always used 0 afaik and the recent traces that epenner@ shared with
us makes it pretty clear that using anything else on android is bad.

[epennerAtGoogle, 2012-11-05 20:51:41]

We have hard data from driver vendors that partial updates are bad. Here's the
two cases we have run into so far:
- Non-aligned update regions can fall into slow-path swizzling which is ~10X as
expensive.
- Updates to in-use textures stalls the GPU until the texture is no longer in
use, or if not it minimally causes a copy-on-write or allocate-on-write which is
much worse than a double-buffered update (for which the back-buffer texture is
not in use).

Disabling partial updates fixes both of those issues, but we might want to
document why. For example, if we had better knowledge that a texture was truly
in-use, we could avoid double-buffered updates to off-screen textures.

[nduca, 2012-11-06 20:14:11]

lgtm if you keep desktop at 12.

[commit-bot: I haz the power, 2012-11-07 00:05:33]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/reveman@chromium.org/11347022/7001

[commit-bot: I haz the power, 2012-11-07 04:40:14]

Change committed as 166347