One more instance of StringBuilder::Append replacing String::Append.
Also remove instances of String::append where StringBuilder can not be used.

Visited top ten sites and no more hits to String::append(WTF::String&).

Review URL: https://codereview.chromium.org/137293005

git-svn-id: svn://svn.chromium.org/blink/trunk@165133 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[FastTextAutosizer] Refactor FTA::inflate() to be internal to FTA

This patch moves inflate() to be a private internal detail of
FastTextAutosizer and relies on beginLayout to call inflate. This
patch also has a minor cleanup removing an untrue FIXME in inflate().

No new tests as this is just a refactoring.

BUG=302005

Review URL: https://codereview.chromium.org/138143004

git-svn-id: svn://svn.chromium.org/blink/trunk@165134 bbb929c8-8fbe-4397-9dbb-9b2b20218538