Navigation transitions: Exposed "setBackgroundOpaque" to ContentViewCore

Navigation transitions: Exposed "setBackgroundOpaque" to ContentViewCore

The navigation transition needs the transition page to render transparently over top the current tab, so we need to expose this call to java.

Design doc: https://docs.google.com/a/chromium.org/document/d/17jg1RRL3RI969cLwbKBIcoGDsPwqaEdBxafGNYGwiY4/edit# 
Implementation details: https://docs.google.com/a/chromium.org/document/d/1kREPtFJaeLoDKwrfmrYTD7DHCdxX1RzFBga2gNY8lyE/edit#heading=h.bng2kpmyvxq5
BUG=370696
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=274587

[bulach, 2014-06-03 10:37:02]

lgtm (but please let sami take a quick look too, thanks!)

[Sami, 2014-06-03 14:55:59]

Sorry for the delay -- I was studying your design docs :) The patch itself lgtm,
but it's not clear to me why Java needs access to this. Is some part of the
transition helper implemented in Java?

[shatch, 2014-06-03 15:00:08]

On 2014/06/03 14:55:59, Sami wrote:
> Sorry for the delay -- I was studying your design docs :) The patch itself
lgtm,
> but it's not clear to me why Java needs access to this. Is some part of the
> transition helper implemented in Java?

Hi Sami! Thanks for taking a look. Yeah I've got a lot of the transition logic
in java. I'll send you guys a link to that review.

[shatch, 2014-06-03 16:32:30]

The CQ bit was checked by simonhatch@chromium.org

[commit-bot: I haz the power, 2014-06-03 16:32:54]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/simonhatch@chromium.org/284413007/40001

[commit-bot: I haz the power, 2014-06-03 19:14:16]

Change committed as 274587