Create MetroViewerProcessHost as a common base for TestMetroViewerProcessHost and ChromeMetroViewerProcessHost

Bringing LaunchViewerAndWaitForConnection() to the common base so that ChromeMetroViewerProcessHost can also benefit from it (required for ash browser tests).

BUG=179830

1st Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=201806
Reverted: https://src.chromium.org/viewvc/chrome?view=rev&revision=201966

R=robertshield@chromium.org, sky@chromium.org

Review URL: https://codereview.chromium.org/14629025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202113 0039d316-1c4b-4281-b951-d872f2087c98
19 files changed