MacViews: Handle three-finger swipe gestures for navigation.

ui/views/cocoa/bridged_content_view.mm

Index: ui/views/cocoa/bridged_content_view.mm
diff --git a/ui/views/cocoa/bridged_content_view.mm b/ui/views/cocoa/bridged_content_view.mm
index b47f522dd7c759f2f1450c06c5eb9b544bfe0806..657e9b5973b59e6dba496b40d923a6ce806c7f5a 100644
--- a/ui/views/cocoa/bridged_content_view.mm
+++ b/ui/views/cocoa/bridged_content_view.mm
@@ -800,6 +800,34 @@ ui::TextEditCommand GetTextEditCommandForMenuAction(SEL action) {
   hostedView_->GetWidget()->OnScrollEvent(&event);
 }
 
+// Called when we get a three-finger swipe, and they're enabled in System
+// Preferences.
+- (void)swipeWithEvent:(NSEvent*)event {
+  if (!hostedView_)
+    return;
+
+  // themblsha: In my testing all three-finger swipes send only a single event
+  // with a value of +/-1 on either axis. Diagonal swipes are not handled by
+  // AppKit.
+
+  // We need to invert deltas in order to match GestureEventDetails's
+  // directions.
+  ui::GestureEventDetails swipeDetails(ui::ET_GESTURE_SWIPE, -[event deltaX],
+                                       -[event deltaY]);
+  swipeDetails.set_device_type(ui::GestureDeviceType::DEVICE_TOUCHPAD);
+  swipeDetails.set_touch_points(3);
+
+  gfx::PointF location = ui::EventLocationFromNative(event);
+  // Note this uses the default unique_touch_event_id of 0 (Swipe events do not
+  // support -[NSEvent eventNumber]). This doesn't seem like a real omission
+  // because the three-finger swipes are instant and can't be tracked anyway.
+  ui::GestureEvent gestureEvent(location.x(), location.y(),
+                                ui::EventFlagsFromNative(event),
+                                ui::EventTimeFromNative(event), swipeDetails);
+
+  hostedView_->GetWidget()->OnGestureEvent(&gestureEvent);
+}
+
 - (void)quickLookWithEvent:(NSEvent*)theEvent {
   if (!hostedView_)
     return;