Update background color when it is transparent.

backgroundColor with 0 alpha is still valid, and FrameView should set the color.
For example, android can set the background color of a WebView to be
transparent. This sets the mainframe base background color to be transparent.

The internal bug is b/15373310
BUG=375864
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175586

[hush (inactive), 2014-06-03 21:05:18]

ptal

[aelias_OOO_until_Jul13, 2014-06-03 21:08:56]

Could you also add a unit test case for this?

[hush (inactive), 2014-06-03 21:25:10]

On 2014/06/03 21:08:56, aelias wrote:
> Could you also add a unit test case for this?

Yes. I will wait for Timothy Loh's comment first to see if this is the right
approach.

[Timothy Loh, 2014-06-04 08:41:31]

On 2014/06/03 21:25:10, hush wrote:
> On 2014/06/03 21:08:56, aelias wrote:
> > Could you also add a unit test case for this?
> 
> Yes. I will wait for Timothy Loh's comment first to see if this is the right
> approach.

I'm not really familiar with this code, but this is probably fine. The check
that used to be here was backgroundColor.isValid(), which I guess I incorrectly
mapped here to backgroundColor.alpha().

[hush (inactive), 2014-06-04 23:29:03]

Hi!
Test is added. Please take a look!

[aelias_OOO_until_Jul13, 2014-06-05 16:55:09]

lgtm, still needs Source/core OWNERS though.

[Timothy Loh, 2014-06-05 17:06:36]

On 2014/06/05 16:55:09, aelias wrote:
> lgtm, still needs Source/core OWNERS though.

Source/core lgtm

[hush (inactive), 2014-06-05 17:10:00]

The CQ bit was checked by hush@chromium.org

[commit-bot: I haz the power, 2014-06-05 17:11:03]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hush@chromium.org/315763003/20001

[commit-bot: I haz the power, 2014-06-05 18:14:30]

Change committed as 175586