r=rods; bug=15478; Added WS_EX_TOOLWINDOW extended style for popup windows

to prevent popups from creating empty task bar buttons.
bug=6061; NS_DISPLAYCHANGE event is now generated when the display depth changes
on WIN32.

widget/public/nsGUIEvent.h

@@ -266,6 +266,9 @@ enum nsDragDropEventStatus {
 // directly to a mouse click or a key press.
 #define NS_CONTROL_CHANGE                (NS_WINDOW_START + 39)
 
+// Indicates the display has changed depth
+#define NS_DISPLAYCHANGED                (NS_WINDOW_START + 40)
+
 
 #define NS_MOUSE_MESSAGE_START          300
 #define NS_MOUSE_MOVE                   (NS_MOUSE_MESSAGE_START)

widget/src/windows/nsWindow.cpp

@@ -624,6 +624,9 @@ nsresult nsWindow::StandardWindowCreate(nsIWidget *aParent,
         mBorderlessParent = parent;
          // Don't set the parent of a popup window. 
         parent = NULL;
+         // WS_EX_TOOLWINDOW prevents a button from being placed on 
+         // the taskbar for the popup window.
+        extendedStyle |= WS_EX_TOOLWINDOW;
       }
 
       if (aInitData->mBorderStyle == eBorderStyle_default) {
@@ -2358,6 +2361,10 @@ PRBool nsWindow::ProcessMessage(UINT msg, WPARAM wParam, LPARAM lParam, LRESULT
         }
         break;
 
+        case WM_DISPLAYCHANGE:
+          DispatchStandardEvent(NS_DISPLAYCHANGED);
+        break;
+
         
         case WM_NOTIFY:
             // TAB change