Bug 1075670 - Update window position in TabParent when window widget is moved. r=smaug

TabParents now register for the MozUpdateWindowPos event on the chrome
TopWindowRoot.  When the window is moved, the OS widget calls WindowMoved on
its listener (the nsWebShellWindow), which sends a MozUpdateWindowPos
event.

xpfe/appshell/nsWebShellWindow.cpp

@@ -71,6 +71,8 @@
 #include "mozilla/DebugOnly.h"
 #include "mozilla/MouseEvents.h"
 
+#include "nsPIWindowRoot.h"
+
 #ifdef XP_MACOSX
 #include "nsINativeMenuService.h"
 #define USE_NATIVE_MENUS
@@ -258,6 +260,15 @@ nsWebShellWindow::WindowMoved(nsIWidget* aWidget, int32_t x, int32_t y)
     pm->AdjustPopupsOnWindowChange(window);
   }
 
+  // Notify all tabs that the widget moved.
+  if (mDocShell && mDocShell->GetWindow()) {
+    nsCOMPtr<EventTarget> eventTarget = mDocShell->GetWindow()->GetTopWindowRoot();
+    nsContentUtils::DispatchChromeEvent(mDocShell->GetDocument(),
+                                        eventTarget,
+                                        NS_LITERAL_STRING("MozUpdateWindowPos"),
+                                        false, false, nullptr);
+  }
+
   // Persist position, but not immediately, in case this OS is firing
   // repeated move events as the user drags the window
   SetPersistenceTimer(PAD_POSITION);