Adds ability for ash_unittests to run in mushrome mode

ash/test/ash_test_suite.h

Index: ash/test/ash_test_suite.h
diff --git a/ash/test/ash_test_suite.h b/ash/test/ash_test_suite.h
index feb5e985723a447678c3bc079dfd77bcf8ba6d13..61f89bcd9174178ef3af00535af372c31f421d3c 100644
--- a/ash/test/ash_test_suite.h
+++ b/ash/test/ash_test_suite.h
@@ -12,6 +12,10 @@
 #include "base/test/test_suite.h"
 #include "ui/aura/env.h"
 
+namespace ui {
+class FakeContextFactory;
+}
+
 namespace ash {
 namespace test {
 
@@ -30,6 +34,9 @@ class AshTestSuite : public base::TestSuite {
 
   base::TestDiscardableMemoryAllocator discardable_memory_allocator_;
 
+  // Only used when running in Config::MUS.

[msw, 2017/03/30 23:06:05]

nit: explain what it's used for?

[sky, 2017/03/30 23:35:46]

Done.

+  std::unique_ptr<ui::FakeContextFactory> context_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(AshTestSuite);
 };