Bug 1168274 part 1 - Avoid triggering window reflow for hiding margins when entering fullscreen on Windows. r=jimm

--HG--
extra : source : a1d29ea748b8d0b8881a5308aebd37149485ec7a

widget/windows/nsWindow.cpp

@@ -2868,7 +2868,9 @@ nsWindow::MakeFullScreen(bool aFullScreen, nsIScreen* aTargetScreen)
     SetSizeMode(mOldSizeMode);
   }
 
-  UpdateNonClientMargins();
+  // If we are going fullscreen, the window size continues to change
+  // and the window will be reflow again then.
+  UpdateNonClientMargins(mSizeMode, /* Reflow */ !aFullScreen);
 
   bool visible = mIsVisible;
   if (mOldSizeMode == nsSizeMode_Normal)