New Tab: fix tab title flickering.

The fix requires two changes:
(1) Change the implementation of WebContents::GetTitle() to use a non-empty 
    title on a pending entry for "initial navigations".
(2) Set the title on pending NTP entries as soon as they're created.

BUG=322099
TESTED=manual, per bug report

Review URL: https://codereview.chromium.org/78443005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237180 0039d316-1c4b-4281-b951-d872f2087c98
5 files changed