Flip the flag to enable smooth screen rotation by default.

ash/rotator/screen_rotation_animator_unittest.cc

Index: ash/rotator/screen_rotation_animator_unittest.cc
diff --git a/ash/rotator/screen_rotation_animator_unittest.cc b/ash/rotator/screen_rotation_animator_unittest.cc
index 19de9cebb14f7c317448a2714d58e5395fa80edf..fa65898242594e67f52b59f6cf3f61ae3dfd0dc4 100644
--- a/ash/rotator/screen_rotation_animator_unittest.cc
+++ b/ash/rotator/screen_rotation_animator_unittest.cc
@@ -12,6 +12,7 @@
 #include "ash/shell.h"
 #include "ash/shell_port.h"
 #include "ash/test/ash_test_base.h"
+#include "ash/test/ash_test_helper.h"
 #include "base/callback_forward.h"
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
@@ -222,6 +223,10 @@ void ScreenRotationAnimatorSmoothAnimationTest::QuitWaitForCopyCallback() {
 
 void ScreenRotationAnimatorSmoothAnimationTest::SetUp() {
   AshTestBase::SetUp();
+  // Resets the commandline will clear all the switches, including
+  // "ash-disable-smooth-screen-rotation", so that we can test the smooth screen
+  // rotation animation. The |animator| is recreated and checking this swtich.
+  ash_test_helper()->reset_commandline();
 
   display_ = display::Screen::GetScreen()->GetPrimaryDisplay();
   if (Shell::GetAshConfig() == Config::MASH) {
@@ -230,8 +235,6 @@ void ScreenRotationAnimatorSmoothAnimationTest::SetUp() {
     return;
   }
 
-  base::CommandLine::ForCurrentProcess()->AppendSwitch(
-      switches::kAshEnableSmoothScreenRotation);
   run_loop_ = base::MakeUnique<base::RunLoop>();
   SetScreenRotationAnimator(display_.id(), run_loop_->QuitWhenIdleClosure(),
                             run_loop_->QuitWhenIdleClosure());