Fix integer overflow.

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc

Index: ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
diff --git a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
index 3b848bc9ddb9aa899dc8eaf96f30a0a97998e5b1..04c5a949777ebd8fa706b78a3b1c60072f78f3ff 100644
--- a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
+++ b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
@@ -1094,7 +1094,13 @@ 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_,