Extend the workaround for broken MacViews window dragging to 10.11.

I didn't catch that it was needed on 10.11 up front because the presence
of the window that shows construction stripes in Chromium builds made
the problem vanish. Weird stuff.

Bug: 838353
Change-Id: I7cf9e352ff51dccfdbc561da58905175dab68742
Reviewed-on: https://chromium-review.googlesource.com/1038624Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Sidney San Martín <sdy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555491}

chrome/browser/ui/views/frame/browser_native_widget_window_mac.mm

@@ -74,10 +74,12 @@ WEAK_IMPORT_ATTRIBUTE
   return NSZeroRect;
 }
 
-// Lets the window be dragged by its title bar on 10.10.
+// Lets the window be dragged by its title bar on 10.11 and older.
 - (void)mouseDown:(NSEvent*)event {
-  if (@available(macOS 10.11, *))
-    ;  // Not needed on 10.11 and up.
+  if (@available(macOS 10.12, *))
+    ;  // Not needed on 10.12 and up.
+  else if (@available(macOS 10.11, *))
+    [self.window performWindowDragWithEvent:event];
   else if (@available(macOS 10.10, *))
     [self.window beginWindowDragWithEvent:event];
   else