cros: Enable ChromeMainTest in mash_browser_tests

It seems to pass now.

Bug: none
Change-Id: I5c6791e407b7436da97788d5f02e47b8f0755ef7
Reviewed-on: https://chromium-review.googlesource.com/1029213
Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554102}

testing/buildbot/filters/mash.browser_tests.filter

@@ -77,10 +77,6 @@
 # Need screenshot support. http://crbug.com/754899
 -ChromeScreenshotGrabberBrowserTest.*
 
-# ChromeBrowserMainExtraPartsAsh: Check failed: views::MusClient::Exists().
--ChromeMainTest.*
--ProfilingBrowserTest.*
-
 # Null immersive_fullscreen_controller_.
 -ChromeNativeAppWindowViewsAuraAshBrowserTest.*