Fix regions generation on windows.

ui/views/win/hwnd_message_handler.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/win/hwnd_message_handler.h"
 
 #include <dwmapi.h>
 #include <oleacc.h>
 #include <shellapi.h>
 #include <wtsapi32.h>
@@ skipping 1115 matching lines @@
     return;
   }
 
   // Changing the window region is going to force a paint. Only change the
   // window region if the region really differs.
   HRGN current_rgn = CreateRectRgn(0, 0, 0, 0);
   int current_rgn_result = GetWindowRgn(hwnd(), current_rgn);
 
   RECT window_rect;
   GetWindowRect(hwnd(), &window_rect);
-  HRGN new_region;
+  HRGN new_region = NULL;

[Wez, 2014/10/27 20:28:39]

While you're here, I'd suggest using ScopedRegion here, and then release() it
below, in the SetWindowRgn call - you can then also get run of the DeleteObject
for new_region. :)  Same applies to current_rgn.

[alex-ac, 2014/10/28 10:38:36]

Done.

   if (custom_window_region_) {
     new_region = ::CreateRectRgn(0, 0, 0, 0);
     ::CombineRgn(new_region, custom_window_region_.Get(), NULL, RGN_COPY);
   } else if (IsMaximized()) {
     HMONITOR monitor = MonitorFromWindow(hwnd(), MONITOR_DEFAULTTONEAREST);
     MONITORINFO mi;
     mi.cbSize = sizeof mi;
     GetMonitorInfo(monitor, &mi);
     RECT work_rect = mi.rcWork;
     OffsetRect(&work_rect, -window_rect.left, -window_rect.top);
     new_region = CreateRectRgnIndirect(&work_rect);
   } else {
     gfx::Path window_mask;
     delegate_->GetWindowMask(gfx::Size(window_rect.right - window_rect.left,
                                        window_rect.bottom - window_rect.top),
                              &window_mask);
-    new_region = gfx::CreateHRGNFromSkPath(window_mask);
+    if (!window_mask.isEmpty())
+      new_region = gfx::CreateHRGNFromSkPath(window_mask);
   }
 
   if (current_rgn_result == ERROR || !EqualRgn(current_rgn, new_region)) {
     // SetWindowRgn takes ownership of the HRGN created by CreateNativeRegion.
     SetWindowRgn(hwnd(), new_region, redraw);
   } else {
     DeleteObject(new_region);
   }
 
   DeleteObject(current_rgn);
@@ skipping 1329 matching lines @@
     SetWindowPos(hwnd(), NULL, 0, 0, 0, 0, flags | SWP_HIDEWINDOW);
     SetWindowPos(hwnd(), NULL, 0, 0, 0, 0, flags | SWP_SHOWWINDOW);
   }
   // WM_DWMCOMPOSITIONCHANGED is only sent to top level windows, however we want
   // to notify our children too, since we can have MDI child windows who need to
   // update their appearance.
   EnumChildWindows(hwnd(), &SendDwmCompositionChanged, NULL);
 }
 
 }  // namespace views