Fix integer overflow.

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc

 // Copyright (c) 2012 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 "ui/views/widget/desktop_aura/desktop_window_tree_host_x11.h"
 
 #include <X11/extensions/shape.h>
 #include <X11/extensions/XInput2.h>
 #include <X11/Xatom.h>
 #include <X11/Xregion.h>
@@ skipping 1076 matching lines @@
 }
 
 bool DesktopWindowTreeHostX11::IsFullscreen() const {
   return is_fullscreen_;
 }
 
 void DesktopWindowTreeHostX11::SetOpacity(float opacity) {
   // X server opacity is in terms of 32 bit unsigned int space, and counts from
   // the opposite direction.
   // XChangeProperty() expects "cardinality" to be long.
-  unsigned long cardinality = static_cast<int>(opacity * 255) * 0x1010101;
+
+  // Scale opacity to [0 .. 255] range.
+  unsigned long opacity_8bit =
+      static_cast<unsigned long>(opacity * 255.0f) & 0xFF;
+  // Use opacity value for all channels.
+  const unsigned long channel_multiplier = 0x1010101;
+  unsigned long cardinality = opacity_8bit * channel_multiplier;
 
   if (cardinality == 0xffffffff) {
     XDeleteProperty(xdisplay_, xwindow_,
                     atom_cache_.GetAtom("_NET_WM_WINDOW_OPACITY"));
   } else {
     XChangeProperty(xdisplay_, xwindow_,
                     atom_cache_.GetAtom("_NET_WM_WINDOW_OPACITY"),
                     XA_CARDINAL, 32,
                     PropModeReplace,
                     reinterpret_cast<unsigned char*>(&cardinality), 1);
@@ skipping 1249 matching lines @@
 
 // static
 DesktopWindowTreeHost* DesktopWindowTreeHost::Create(
     internal::NativeWidgetDelegate* native_widget_delegate,
     DesktopNativeWidgetAura* desktop_native_widget_aura) {
   return new DesktopWindowTreeHostX11(native_widget_delegate,
                                       desktop_native_widget_aura);
 }
 
 }  // namespace views