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..67a2a5e850362c7779d2535c19715b22bac7ff2f 100644
--- a/chrome/browser/ui/views/frame/browser_view.cc
+++ b/chrome/browser/ui/views/frame/browser_view.cc
@@ -1938,6 +1938,29 @@ 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) {

[tapted, 2017/02/15 22:25:52]

Inferring the return type of a lambda is a C++14 feature.. I doubt MSVC will
like this. This is #if guarded so MSVC might not see it, but I don't think we
should be relying on this just yet.

I think sky's suggestion is more idiomatic for chrome -- just pass an int* and
return a bool.

+    if (event->details().type() == ui::ET_GESTURE_SWIPE) {
+      if (event->details().swipe_left())
+        return base::Optional<int>(IDC_BACK);
+      else if (event->details().swipe_right())
+        return base::Optional<int>(IDC_FORWARD);
+    }
+    return base::Optional<int>();
+  };
+
+  auto command = get_gesture_command(event);
+  if (command.has_value() && chrome::IsCommandEnabled(browser(), *command)) {
+    chrome::ExecuteCommandWithDisposition(
+        browser(), *command, ui::DispositionFromEventFlags(event->flags()));
+    return;
+  }
+#endif  // OS_MACOSX
+
+  ClientView::OnGestureEvent(event);
+}
+
 void BrowserView::ViewHierarchyChanged(
     const ViewHierarchyChangedDetails& details) {
   if (!initialized_ && details.is_add && details.child == this && GetWidget()) {