Fix views compilation on Linux with toolkit_views=1.
Fix views compilation on Linux with toolkit_views=1.

This fixes the following error:
../../ui/views/bubble/bubble_delegate.cc: In function ‘views::Widget* views::<unnamed>::CreateBubbleWidget(views::BubbleDelegateView*, views::Widget*)’:
../../ui/views/bubble/bubble_delegate.cc:29:50: error: cannot convert ‘GtkWindow*’ to ‘GtkWidget*’ in assignment

BUG=113010
TEST=none

Review URL: https://chromiumcodereview.appspot.com/9317111

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@120794 0039d316-1c4b-4281-b951-d872f2087c98

gavinp/chromium,ropik/chromium,ropik/chromium,yitian134/chromium,adobe/chromium,gavinp/chromium,adobe/chromium,yitian134/chromium,gavinp/chromium,gavinp/chromium,ropik/chromium,adobe/chromium,adobe/chromium,ropik/chromium,yitian134/chromium,yitian134/chromium,ropik/chromium,gavinp/chromium,ropik/chromium,yitian134/chromium,gavinp/chromium,yitian134/chromium,ropik/chromium,yitian134/chromium,adobe/chromium,ropik/chromium,ropik/chromium,gavinp/chromium,adobe/chromium,adobe/chromium,adobe/chromium,adobe/chromium,yitian134/chromium,gavinp/chromium,yitian134/chromium,gavinp/chromium,adobe/chromium,yitian134/chromium,adobe/chromium,gavinp/chromium