Views Omnibox: Only select all on update with previous selection.

BUG=343852
TEST=With a clear selection clipboard on Linux Aura; type "chrome://apps"+[ENTER]; open a new tab and middle click in the empty omnibox; no text should be pasted. No selection/update or other Omnibox behavior regressions.
R=pkasting@chromium.org

Review URL: https://codereview.chromium.org/164753008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251516 0039d316-1c4b-4281-b951-d872f2087c98
rAc: minimal crash fix for bug 342990.

BUG=342990
TEST=no more crashes
R=estade@chromium.org

Review URL: https://codereview.chromium.org/165223002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251517 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251517