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>
 #include <X11/Xutil.h>
 
+#include <algorithm>
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/location.h"
 #include "base/memory/ptr_util.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ skipping 1062 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;

[sky, 2017/01/03 17:54:27]

Can you outline where this goes wrong? Before my change the code was this:

void DesktopWindowTreeHostX11::SetOpacity(unsigned char opacity) {
  unsigned long cardinality = opacity * 0x1010101;

But as long as opacity (in the new code) is 0-1, shouldn't this be the same?

+
+  // Clamp opacity to [0.0 .. 1.0] range.
+  float clamped_opacity = std::max(0.0f, std::min(1.0f, opacity));

[sky, 2017/01/03 17:54:27]

We don't do this anywhere else. It's assumed the value is 0-1. A DCHECK here is
fine (or better yet in Widget::SetOpacity() which is generally the entry point
for this.

+  // Scale opacity to [0 .. 255] range.
+  unsigned long opacity_8bit =
+      static_cast<unsigned long>(clamped_opacity * 255.0f);
+  // 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