Run exo tests in parallel

BUG=None
TEST=All tests still should pass

Change-Id: I8a2cc5598baaa9692a33a79767f93869e5a75b9b
Reviewed-on: https://chromium-review.googlesource.com/657622Reviewed-by: David Reveman <reveman@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#500712}

components/exo/test/run_all_unittests.cc

@@ -17,7 +17,7 @@ int main(int argc, char** argv) {
   mojo::edk::Init();
 #endif
 
-  return base::LaunchUnitTestsSerially(
+  return base::LaunchUnitTests(
       argc, argv,
       base::Bind(&ash::AshTestSuite::Run, base::Unretained(&test_suite)));
 }