Removes mouse listeners from UserInputMonitor.

media/base/user_input_monitor_mac.cc

Index: media/base/user_input_monitor_mac.cc
diff --git a/media/base/user_input_monitor_mac.cc b/media/base/user_input_monitor_mac.cc
index 12a4ac8f361d6eae2152de0975a8c1c23b8602b9..a85a334954e04ec1a3119f2a6105f9ffe9072b14 100644
--- a/media/base/user_input_monitor_mac.cc
+++ b/media/base/user_input_monitor_mac.cc
@@ -23,8 +23,6 @@ class UserInputMonitorMac : public UserInputMonitor {
  private:
   void StartKeyboardMonitoring() override;
   void StopKeyboardMonitoring() override;
-  void StartMouseMonitoring() override;
-  void StopMouseMonitoring() override;
 
   DISALLOW_COPY_AND_ASSIGN(UserInputMonitorMac);
 };
@@ -44,12 +42,6 @@ void UserInputMonitorMac::StartKeyboardMonitoring() {}
 
 void UserInputMonitorMac::StopKeyboardMonitoring() {}
 
-// TODO(jiayl): add the impl.
-void UserInputMonitorMac::StartMouseMonitoring() { NOTIMPLEMENTED(); }
-
-// TODO(jiayl): add the impl.
-void UserInputMonitorMac::StopMouseMonitoring() { NOTIMPLEMENTED(); }
-
 }  // namespace
 
 std::unique_ptr<UserInputMonitor> UserInputMonitor::Create(