Fix a crash seen at times when chrome in desktop mode attempts to activate Chrome in Windows 8 mode…

Fix a crash seen at times when chrome in desktop mode attempts to activate Chrome in Windows 8 mode. The crash
occurs because we attempt to initiate a navigation when there are no frame windows registered with the metro driver.

Fix is to ignore the navigation request in this case.

I also updated the ChromeUrlLaunchHandler::GetUrlFromLaunchArgs function to return the chrome://newtab url if the verb
coming in is opennewwindow. This should address bug http://code.google.com/p/chromium/issues/detail?id=135122

BUG=155281, 135122
R=cpu
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=162269

[cpu_(ooo_6.6-7.5), 2012-10-16 21:55:15]

lgtm