Only allow to lock the mouse when the tab is in fullscreen mode.

ppapi/examples/mouse_lock/mouse_lock.cc

 // Copyright (c) 2011 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 <cmath>
 #include <stdarg.h>
 #include <stdio.h>
 
 #include "ppapi/c/dev/ppb_console_dev.h"
 #include "ppapi/c/ppb_input_event.h"
@@ skipping 35 matching lines @@
   }
 
   virtual bool HandleInputEvent(const pp::InputEvent& event) {
     switch (event.GetType()) {
       case PP_INPUTEVENT_TYPE_MOUSEDOWN: {
         pp::MouseInputEvent mouse_event(event);
         if (mouse_event.GetButton() == PP_INPUTEVENT_MOUSEBUTTON_LEFT &&
             !mouse_locked_) {
           LockMouse(
               callback_factory_.NewRequiredCallback(&MyInstance::DidLockMouse));
-        } else if (mouse_event.GetButton() == PP_INPUTEVENT_MOUSEBUTTON_RIGHT &&
-                   mouse_locked_) {
+        } else if (
+            mouse_event.GetButton() == PP_INPUTEVENT_MOUSEBUTTON_MIDDLE &&
+            mouse_locked_) {
           UnlockMouse();
         }
         return true;
       }
       case PP_INPUTEVENT_TYPE_MOUSEMOVE: {
         pp::MouseInputEvent mouse_event(event);
         mouse_movement_ = mouse_event.GetMovement();
         static unsigned int i = 0;
         Log(PP_LOGLEVEL_LOG, "[%d] movementX: %d; movementY: %d\n", i++,
             mouse_movement_.x(), mouse_movement_.y());
@@ skipping 195 matching lines @@
 
 namespace pp {
 
 // Factory function for your specialization of the Module object.
 Module* CreateModule() {
   return new MyModule();
 }
 
 }  // namespace pp