Switch platform apps from a declarative launch container to handling an onLaunched event.

Switch platform apps from a declarative launch container to handling an onLaunched event. 

Platform apps must now have a background page. For the handling of launches, 
the background page registers an onLaunched event handler, and creates UI 
as appropriate via the chrome.windows.* API. 

Updates all tests to use the new window model. 

Also makes created shell window respect the bounds that were passed into the 
chrome.windows.create() call. 

Also fixes bug by resizing windows in PlatformAppBrowserTest.WindowsApi to a 
size that matches the Aura grid. 

This CL was originally written by mihaip@chromium.org - the original is:
  http://codereview.chromium.org/9969087/


TBR=mihaip@chromium.org

BUG=119410
TEST=Platform apps should now require a background page.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=133555