Fix ArcActiveDirectoryEnrollmentTokenFetcherBrowserTest.SamlFlowSucceedsWithAuthRetry

Handle setWindowBounds for FakeArcSupport (just do nothing). It fails
there if mash is enabled.

Bug: 859503
Change-Id: Icb99100691de2dfed753b1afbd935c0be10117eb
Reviewed-on: https://chromium-review.googlesource.com/1122620Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Lutz Justen <ljusten@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571891}

chrome/browser/chromeos/arc/extensions/fake_arc_support.cc

@@ -200,6 +200,8 @@ void FakeArcSupport::PostMessageFromNativeHost(
     }
   } else if (action == "closeWindow") {
     // Do nothing as emulation.
+  } else if (action == "setWindowBounds") {
+    // Do nothing as emulation.
   } else {
     // Unknown or unsupported action.
     NOTREACHED() << message_string;