Avoid crash when checking gamepad user activation

The Gamepad API may be invoked after the frame has been detached, in
which case GetPage() and GetFrame() will be null. If the Gamepad API
was uninitialized before the frame was detached, the gamepads_ buffer
may also be null.

This CL adds more null checks to the user activation check to ensure
we do not try to access the page after it has been detached.

BUG=852517

Change-Id: I4d8152a9a16a027719d31150bd1b7687fdf991a0
Reviewed-on: https://chromium-review.googlesource.com/1101926Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Matt Reynolds <mattreynolds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567737}

third_party/blink/renderer/modules/gamepad/navigator_gamepad.cc

@@ -65,12 +65,14 @@ void HasGamepadConnectionChanged(const String& old_id,
     *gamepad_lost = id_changed || (old_connected && !new_connected);
 }
 
-bool HasUserActivation(GamepadList& gamepads) {
+bool HasUserActivation(GamepadList* gamepads) {
+  if (!gamepads)
+    return false;
   // A button press counts as a user activation if the button's value is greater
   // than the activation threshold. A threshold is used so that analog buttons
   // or triggers do not generate an activation from a light touch.
-  for (size_t pad_index = 0; pad_index < gamepads.length(); ++pad_index) {
-    Gamepad* pad = gamepads.item(pad_index);
+  for (size_t pad_index = 0; pad_index < gamepads->length(); ++pad_index) {
+    Gamepad* pad = gamepads->item(pad_index);
     if (pad) {
       const GamepadButtonVector& buttons = pad->buttons();
       for (size_t i = 0; i < buttons.size(); ++i) {
@@ -204,9 +206,10 @@ GamepadList* NavigatorGamepad::Gamepads() {
 
   SampleAndCheckConnectedGamepads();
 
-  // Allow gamepad button presses to qualify as user activations.
-  if (RuntimeEnabledFeatures::UserActivationV2Enabled() &&
-      GetPage()->IsPageVisible() && HasUserActivation(*gamepads_)) {
+  // Allow gamepad button presses to qualify as user activations if the page is
+  // visible.
+  if (RuntimeEnabledFeatures::UserActivationV2Enabled() && GetFrame() &&
+      GetPage() && GetPage()->IsPageVisible() && HasUserActivation(gamepads_)) {
     Frame::NotifyUserActivation(GetFrame(), UserGestureToken::kNewGesture);
   }