Coverity: Check return of TabProxy::GoForward, GoBack, etc
Coverity: Check return of TabProxy::GoForward, GoBack, etc

CID=5709,5708,5706,5705,5704,5703,5702,5701,5700
BUG=none
TEST=ran the tests

Review URL: http://codereview.chromium.org/256067

git-svn-id: http://src.chromium.org/svn/trunk/src@28340 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 04a49c7966fc95160cc6f0df8385687890500a07
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser