[Mac] Magnifying glass in keyword-search bubble.

Abstract the image-in-attributed-string code into a helper function so
everyone makes the same mistakes.  The keyword-search string's
baseline became wrong at some point, adjust it to match the rest of
the field.

BUG=37865
TEST=Type "google.com" until "press tab to search" appears, hit TAB.  "Search Google:" bubble should have a magnifying glass on the LHS.
TEST=Add a bunch of text to search.  Resizing smaller should first remove the image, then change to shorter text ("Search Go..." or somesuch).

Review URL: http://codereview.chromium.org/1581011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@43540 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed