Add more options to --screen-config flag.

Allow the user to specify more options for each DisplaySnapshot created
by FakeDisplayDelegate. Alternate resolutions, different refresh rates
and various option toggles are added.

Add tests for FakeDisplaySnapshot that verify the display specification
string parsing.

BUG=611475

Review-Url: https://codereview.chromium.org/2395873002
Cr-Commit-Position: refs/heads/master@{#425084}
13 files changed