Flip the flag to enable smooth screen rotation by default.

ash/display/display_configuration_controller.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/display/display_configuration_controller.h"
 
 #include "ash/display/display_animator.h"
 #include "ash/display/display_animator_chromeos.h"
 #include "ash/display/display_util.h"
 #include "ash/rotator/screen_rotation_animator.h"
@@ skipping 13 matching lines @@
 // displays. It will be overriden by |kAfterDisplayChangeThrottleTimeoutMs|
 // when the display change happens, so the actual timeout is much shorter.
 const int64_t kAfterDisplayChangeThrottleTimeoutMs = 500;
 const int64_t kCycleDisplayThrottleTimeoutMs = 4000;
 const int64_t kSetPrimaryDisplayThrottleTimeoutMs = 500;
 
 }  // namespace
 
 namespace ash {
 
+namespace {
+
+bool CanAnimate(ScreenRotationAnimator* animator) {
+  return animator && animator->CanAnimate();
+}
+
+}  // namespace
+
 class DisplayConfigurationController::DisplayChangeLimiter {
  public:
   DisplayChangeLimiter() : throttle_timeout_(base::Time::Now()) {}
 
   void SetThrottleTimeout(int64_t throttle_ms) {
     throttle_timeout_ =
         base::Time::Now() + base::TimeDelta::FromMilliseconds(throttle_ms);
   }
 
   bool IsThrottled() const { return base::Time::Now() < throttle_timeout_; }
@@ skipping 53 matching lines @@
 }
 
 void DisplayConfigurationController::SetDisplayRotation(
     int64_t display_id,
     display::Display::Rotation rotation,
     display::Display::RotationSource source) {
   if (display_manager_->GetDisplayInfo(display_id).GetActiveRotation() ==
       rotation)
     return;
 
+  ScreenRotationAnimator* screen_rotation_animator = nullptr;
   if (display_manager_->IsDisplayIdValid(display_id)) {
-    ScreenRotationAnimator* screen_rotation_animator =
-        GetScreenRotationAnimatorForDisplay(display_id);
+    screen_rotation_animator = GetScreenRotationAnimatorForDisplay(display_id);
+  }
+  if (CanAnimate(screen_rotation_animator)) {
     screen_rotation_animator->Rotate(rotation, source);
   } else {
-    DCHECK(!rotation_animator_map_.count(display_id));
     display_manager_->SetDisplayRotation(display_id, rotation, source);
   }
 }
 
 void DisplayConfigurationController::SetPrimaryDisplayId(int64_t display_id) {
   if (display_manager_->GetNumDisplays() <= 1 || IsLimited())
     return;
 
   SetThrottleTimeout(kSetPrimaryDisplayThrottleTimeoutMs);
   if (display_animator_) {
@@ skipping 57 matching lines @@
     return iter->second.get();
 
   auto animator = base::MakeUnique<ScreenRotationAnimator>(display_id);
   ScreenRotationAnimator* result = animator.get();
   rotation_animator_map_.insert(
       std::make_pair(display_id, std::move(animator)));
   return result;
 }
 
 }  // namespace ash