Mac: Enable two finger double-tap smart zoom

content/browser/renderer_host/render_widget_host_view_mac.mm

Index: content/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
index 58b9d642b7489f3814672ec3a0db33df5ecfdbba..2a617d1b0d23a510eed209b37f7f14cbb133816b 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -2271,6 +2271,13 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
   [responderDelegate_ touchesEndedWithEvent:event];
 }
 
+- (void)smartMagnifyWithEvent:(NSEvent*)event {
+  const WebGestureEvent& smartMagnifyEvent =
+      WebInputEventFactory::gestureEvent(event, self);
+  renderWidgetHostView_->render_widget_host_->ForwardGestureEvent(
+      smartMagnifyEvent);
+}
+
 // This is invoked only on 10.8 or newer when the user taps a word using
 // three fingers.
 - (void)quickLookWithEvent:(NSEvent*)event {