ozone/drm: Don't EnableController unnecessarily

In UpdateControllerToWindowMapping, EnableController only needs to
be called if the window is moving from one controller to another. Check
if the window was not associated with a controller, and do not call
EnableController in that case.

BUG=888561

Change-Id: Ie077c13c804dbbce9315c75b6ad22a3ec4d6c8d8
Reviewed-on: https://chromium-review.googlesource.com/c/1263415Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Commit-Queue: Drew Davenport <ddavenport@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597234}

ui/ozone/platform/drm/gpu/screen_manager.cc

@@ -341,8 +341,8 @@ void ScreenManager::UpdateControllerToWindowMapping() {
     if (it != window_to_controller_map.end())
       controller = it->second;
 
-    bool should_enable =
-        controller && pair.second->GetController() != controller;
+    bool should_enable = controller && pair.second->GetController() &&
+                         pair.second->GetController() != controller;
     pair.second->SetController(controller);
 
     // If we're moving windows between controllers modeset the controller

ui/ozone/platform/drm/gpu/screen_manager_unittest.cc

@@ -572,6 +572,26 @@ TEST_F(ScreenManagerTest, DISABLED_RejectBufferWithIncompatibleModifiers) {
   window->Shutdown();
 }
 
+TEST_F(ScreenManagerTest, ConfigureDisplayControllerShouldModesetOnce) {
+  std::unique_ptr<ui::DrmWindow> window(
+      new ui::DrmWindow(1, device_manager_.get(), screen_manager_.get()));
+  window->Initialize();
+  window->SetBounds(GetPrimaryBounds());
+  screen_manager_->AddWindow(1, std::move(window));
+
+  screen_manager_->AddDisplayController(drm_, kPrimaryCrtc, kPrimaryConnector);
+  screen_manager_->ConfigureDisplayController(
+      drm_, kPrimaryCrtc, kPrimaryConnector, GetPrimaryBounds().origin(),
+      kDefaultMode);
+
+  // When a window that had no controller becomes associated with a new
+  // controller, expect the crtc to be modeset once.
+  EXPECT_EQ(drm_->get_set_crtc_call_count(), 1);
+
+  window = screen_manager_->RemoveWindow(1);
+  window->Shutdown();
+}
+
 TEST(ScreenManagerTest2, ShouldNotHardwareMirrorDifferentDrmDevices) {
   auto gbm_device1 = std::make_unique<MockGbmDevice>();
   auto drm_device1 =