[Windows] Maximize the window over the taskbar in the fullscreen mode.

It allows the users to close the fullscreen application.
This is a temporary solution. Metro driver will be used to make
Crosswalk applications work like Windows universal application,
which is in src/win8/metro_driver of Chromium source code.

BUG=XWALK-4861

Author: Joone Hur

ui/views/widget/widget.cc

@@ -693,6 +693,9 @@ void Widget::SetVisibleOnAllWorkspaces(bool always_visible) {
 
 void Widget::Maximize() {
   native_widget_->Maximize();
+#if defined(OS_WIN)
+  saved_show_state_ = ui::SHOW_STATE_MAXIMIZED;
+#endif
 }
 
 void Widget::Minimize() {

ui/views/win/hwnd_message_handler.cc

@@ -594,6 +594,17 @@ void HWNDMessageHandler::ShowWindowWithState(ui::WindowShowState show_state) {
   }
 
   ShowWindow(hwnd(), native_show_state);
+
+  // Overlap the taskbar and remove the minimize and maximize button in
+  // the title bar for the fullscreen mode.
+  if (native_show_state == SW_SHOWMAXIMIZED) {
+    LONG style = GetWindowLong(hwnd(), GWL_STYLE);
+    SetWindowLong(hwnd(), GWL_STYLE, style & ~(WS_MAXIMIZEBOX |
+        WS_MINIMIZEBOX));
+    SetWindowPos(hwnd(), HWND_TOPMOST, 0, 0, GetSystemMetrics(SM_CXSCREEN),
+        GetSystemMetrics(SM_CYSCREEN), SWP_DRAWFRAME | SWP_FRAMECHANGED);
+  }
+
   // When launched from certain programs like bash and Windows Live Messenger,
   // show_state is set to SW_HIDE, so we need to correct that condition. We
   // don't just change show_state to SW_SHOWNORMAL because MSDN says we must