Fallback on system locale for font selection

If two character have the same unicode, Font will depend on the language attribute.
But if Font do not get locale from net response and Html tag, it should be defaultLanguage.
It should not only be EN.

BUG=609043

Review-Url: https://codereview.chromium.org/1955523002
Cr-Commit-Position: refs/heads/master@{#394093}
4 files changed