[WebView] Fix issue with transparent background.

[WebView] Fix issue with transparent background.

Always make the background of the layer tree host
in the parent compositor transparent to avoid
covering up the background color of the WebView.

BUG=391462
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=281427

[boliu, 2014-07-04 14:32:23]

lgtm

This is the right thing to do. I wasn't thinking clearly when I told you
transparent won't always work...actually I don't remember exactly what I said.

One nit in description, this is the parent compositor

You'll need a crbug if you want this merged

[Ignacio Solla, 2014-07-04 14:40:04]

On 2014/07/04 14:32:23, boliu wrote:
> lgtm
> 
> This is the right thing to do. I wasn't thinking clearly when I told you
> transparent won't always work...actually I don't remember exactly what I said.
> 
> One nit in description, this is the parent compositor
> 
> You'll need a crbug if you want this merged

I have fixed the description and created the crbug now.

[Ignacio Solla, 2014-07-04 14:40:08]

The CQ bit was checked by igsolla@chromium.org

[commit-bot: I haz the power, 2014-07-04 14:40:39]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/igsolla@chromium.org/368273008/1

[commit-bot: I haz the power, 2014-07-04 18:34:28]

Change committed as 281427