Make Page::history() return a reference

This CL makes the calling code look safer as it can never return null.

Review URL: https://codereview.chromium.org/90153004

git-svn-id: svn://svn.chromium.org/blink/trunk@162734 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Have Locale::create() take a String in argument

Have Locale::create() take a String in argument instead of an AtomicString
as the implementation then converts it back to a String anyway.

This also avoids uselessly converting a String a an AtomicString in one
of the callers: Locale::defaultLocale(). The languages are stored / exposed
as Strings in Language.*

R=abarth
BUG=323739

Review URL: https://codereview.chromium.org/90243005

git-svn-id: svn://svn.chromium.org/blink/trunk@162735 bbb929c8-8fbe-4397-9dbb-9b2b20218538