X11: Fix msan use-of-uninitialized-value error

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 1660 matching lines @@
       ToPixelRect(gfx::Rect(native_widget_delegate_->GetMinimumSize())).size();
   gfx::Size maximum_in_pixels =
       ToPixelRect(gfx::Rect(native_widget_delegate_->GetMaximumSize())).size();
   if (min_size_in_pixels_ == minimum_in_pixels &&
       max_size_in_pixels_ == maximum_in_pixels)
     return;
 
   min_size_in_pixels_ = minimum_in_pixels;
   max_size_in_pixels_ = maximum_in_pixels;
 
   XSizeHints hints;

[Nico, 2017/03/11 00:40:44]

= {} here to zero out all the fields doesn't work?

[Tom (Use chromium acct), 2017/03/11 00:45:35]

That would work too, but it's unnecessary because Xlib only reads fields in
XSizeHints if the appropriate bit is set in |flags|.

Having it this way ensures that msan errors will be detected in the case of
setting a big in |flags|, and forgetting to set the corresponding field.

+  hints.flags = 0;
   long supplied_return;
   XGetWMNormalHints(xdisplay_, xwindow_, &hints, &supplied_return);
 
   if (minimum_in_pixels.IsEmpty()) {
     hints.flags &= ~PMinSize;
   } else {
     hints.flags |= PMinSize;
     hints.min_width = min_size_in_pixels_.width();
     hints.min_height = min_size_in_pixels_.height();
   }
@@ skipping 661 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