Mac: Don't manually start frame drag on 10.12+

On 10.12, the window server is fine initiating a drag without this, so
we end up with two drags starting.

This actually doesn't fix the teleporting windows bug, but it can't help!

Bug: 897274
Change-Id: I2e181659c504c90db0a0928747f5485419728fe8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2207980Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771854}

components/remote_cocoa/app_shim/native_widget_mac_nswindow.mm

@@ -5,6 +5,7 @@
 #import "components/remote_cocoa/app_shim/native_widget_mac_nswindow.h"
 
 #include "base/mac/foundation_util.h"
+#include "base/mac/mac_util.h"
 #include "base/trace_event/trace_event.h"
 #import "components/remote_cocoa/app_shim/native_widget_ns_window_bridge.h"
 #include "components/remote_cocoa/app_shim/native_widget_ns_window_host_helper.h"
@@ -59,7 +60,7 @@
 
 @implementation NativeWidgetMacNSWindowTitledFrame
 - (void)mouseDown:(NSEvent*)event {
-  if (self.window.isMovable)
+  if (base::mac::IsAtMostOS10_11() && self.window.isMovable)
     [self cr_mouseDownOnFrameView:event];
   [super mouseDown:event];
 }