Create U2F tab helper and remove U2F related methods from Tab class

Made U2FController more of implementation details. with U2FTabHelper as the
public class to be used.
Added tests to U2FTabHelperTest to test the javascript execution. instead of mocking the method (was mocked in
u2f_controller_unittest). Also simplified all the existing unit tests.

Bug: 902048
Change-Id: Ife7ac7605bb7bb0e236095dd42871152ea696cfb
Commit-Queue: Mohammad Refaat <>
Reviewed-by: Eugene But <>
Cr-Commit-Position: refs/heads/master@{#638044}
15 files changed