chromeos: Makes AshTestBase/Helper target mash when appropriate

ash/common/test/ash_test.cc

Index: ash/common/test/ash_test.cc
diff --git a/ash/common/test/ash_test.cc b/ash/common/test/ash_test.cc
index 245ce6b5b67fe5139236eaed08b9a02b22a06f42..ba087ec2cf9e4dcf62b382fc230d20fc8895b3c8 100644
--- a/ash/common/test/ash_test.cc
+++ b/ash/common/test/ash_test.cc
@@ -105,6 +105,10 @@ display::Display AshTest::GetSecondaryDisplay() {
 bool AshTest::SetSecondaryDisplayPlacement(
     display::DisplayPlacement::Position position,
     int offset) {
+  if (WmShell::Get()->IsRunningInMash()) {
+    NOTIMPLEMENTED();
+    return false;
+  }
   return test_impl_->SetSecondaryDisplayPlacement(position, offset);
 }