MacViews: Handle three-finger swipe gestures for navigation.

chrome/browser/ui/views/frame/browser_view.cc

Index: chrome/browser/ui/views/frame/browser_view.cc
diff --git a/chrome/browser/ui/views/frame/browser_view.cc b/chrome/browser/ui/views/frame/browser_view.cc
index f4dbf87a9b3440d7ce19808cf32bf6b2c92f3fe7..76eef5e3f426c307069403dc44488d0f62601250 100644
--- a/chrome/browser/ui/views/frame/browser_view.cc
+++ b/chrome/browser/ui/views/frame/browser_view.cc
@@ -1938,6 +1938,31 @@ void BrowserView::Layout() {
       IsToolbarVisible() ? FocusBehavior::ALWAYS : FocusBehavior::NEVER);
 }
 
+void BrowserView::OnGestureEvent(ui::GestureEvent* event) {
+#if defined(OS_MACOSX)
+  auto get_gesture_command = [](ui::GestureEvent* event,
+                                base::Optional<int>* command) {
+    if (event->details().type() == ui::ET_GESTURE_SWIPE) {
+      if (event->details().swipe_left())
+        *command = IDC_BACK;
+      else if (event->details().swipe_right())
+        *command = IDC_FORWARD;
+    }
+    return command->has_value();
+  };
+
+  base::Optional<int> command;
+  if (get_gesture_command(event, &command) &&
+      chrome::IsCommandEnabled(browser(), *command)) {
+    chrome::ExecuteCommandWithDisposition(
+        browser(), *command, ui::DispositionFromEventFlags(event->flags()));
+    return;
+  }
+#endif  // OS_MACOSX
+
+  ClientView::OnGestureEvent(event);
+}

[tapted, 2017/02/20 23:14:21]

I'm undecided about base::Optional and the lambda here. Older code would use
int* and a function in an anonymous namespace. The new approach has merit, but
it will be unfamiliar for some developers. So, no objection from me, but I am
not owner here :)

+
 void BrowserView::ViewHierarchyChanged(
     const ViewHierarchyChangedDetails& details) {
   if (!initialized_ && details.is_add && details.child == this && GetWidget()) {