Fix regions generation on windows.

ui/views/win/hwnd_message_handler.cc

Index: ui/views/win/hwnd_message_handler.cc
diff --git a/ui/views/win/hwnd_message_handler.cc b/ui/views/win/hwnd_message_handler.cc
index 1544507ef39740982de458fcff8f71dd0b069b6c..8685e1fe044223f10be3243709a27bf1777573ce 100644
--- a/ui/views/win/hwnd_message_handler.cc
+++ b/ui/views/win/hwnd_message_handler.cc
@@ -1133,7 +1133,7 @@ void HWNDMessageHandler::ResetWindowRegion(bool force, bool redraw) {
 
   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);
@@ -1150,7 +1150,8 @@ void HWNDMessageHandler::ResetWindowRegion(bool force, bool redraw) {
     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)) {