wake lock: Do not dispatch events if the context has been destroyed.

Both WakeLock and WakeLockSentinel inherit from ContextLifecycleObserver,
but by design a WakeLock is always created before a WakeLockSentinel, and
thus its ContextDestroyed() implementation is called before
WakeLockSentinel's.

This can result in the following call chain:
1. WakeLock::ContextDestroyed()
2. WakeLockManager::ClearWakeLocks()
3. WakeLockSentinel::DoRelease()

if a WakeLockSentinel has an event handler, DoRelease() will try to dispatch
an event after the context has been destroyed, as
WakeLockSentinel::ContextDestroyed(), which calls RemoveAllEventListeners(),
has not been called yet.

We now check if we have a usable context before dispatching events.

WakeLockSentinelTest.ContextDestruction() has been augmented and now tests
the entire flow (i.e. starting with a WakeLock object) rather than just
context destruction when a WakeLockSentinel is present.

Bug: 1023477
Change-Id: I3211d60d624456b950a884771c3fba79a4f8fa8d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917359
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Auto-Submit: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715406}

third_party/blink/renderer/modules/wake_lock/wake_lock.h

@@ -73,6 +73,7 @@ class MODULES_EXPORT WakeLock final : public ScriptWrappable,
   // record per responsible document [...] internal slots.
   Member<WakeLockManager> managers_[kWakeLockTypeCount];
 
+  FRIEND_TEST_ALL_PREFIXES(WakeLockSentinelTest, ContextDestruction);
   FRIEND_TEST_ALL_PREFIXES(WakeLockTest, RequestWakeLockGranted);
   FRIEND_TEST_ALL_PREFIXES(WakeLockTest, RequestWakeLockDenied);
   FRIEND_TEST_ALL_PREFIXES(WakeLockTest, LossOfDocumentActivity);

third_party/blink/renderer/modules/wake_lock/wake_lock_sentinel.cc

@@ -85,6 +85,11 @@ void WakeLockSentinel::DoRelease() {
   manager_->UnregisterSentinel(this);
   manager_.Clear();
 
+  // This function may be called on ExecutionContext destruction. Events should
+  // not be dispatched in this case.
+  if (!GetExecutionContext() || GetExecutionContext()->IsContextDestroyed())
+    return;
+
   // 6. Queue a task to fire an event named "release" at lock.
   DispatchEvent(*Event::Create(event_type_names::kRelease));
 }

third_party/blink/renderer/modules/wake_lock/wake_lock_sentinel_test.cc

@@ -12,6 +12,7 @@
 #include "third_party/blink/renderer/core/dom/document.h"
 #include "third_party/blink/renderer/core/dom/events/native_event_listener.h"
 #include "third_party/blink/renderer/modules/event_target_modules_names.h"
+#include "third_party/blink/renderer/modules/wake_lock/wake_lock.h"
 #include "third_party/blink/renderer/modules/wake_lock/wake_lock_manager.h"
 #include "third_party/blink/renderer/modules/wake_lock/wake_lock_test_utils.h"
 #include "third_party/blink/renderer/platform/heap/handle.h"
@@ -85,10 +86,24 @@ TEST(WakeLockSentinelTest, ContextDestruction) {
   MockWakeLockService wake_lock_service;
   WakeLockTestingContext context(&wake_lock_service);
 
-  auto* sentinel = MakeGarbageCollected<WakeLockSentinel>(
-      context.GetScriptState(), WakeLockType::kScreen,
-      MakeGarbageCollected<WakeLockManager>(context.GetDocument(),
-                                            WakeLockType::kScreen));
+  context.GetPermissionService().SetPermissionResponse(
+      WakeLockType::kScreen, mojom::blink::PermissionStatus::GRANTED);
+
+  auto* screen_resolver =
+      MakeGarbageCollected<ScriptPromiseResolver>(context.GetScriptState());
+  ScriptPromise screen_promise = screen_resolver->Promise();
+
+  auto* wake_lock = MakeGarbageCollected<WakeLock>(*context.GetDocument());
+  wake_lock->DoRequest(WakeLockType::kScreen, screen_resolver);
+
+  WakeLockManager* manager =
+      wake_lock->managers_[static_cast<size_t>(WakeLockType::kScreen)];
+  ASSERT_TRUE(manager);
+
+  context.WaitForPromiseFulfillment(screen_promise);
+  auto* sentinel = ScriptPromiseUtils::GetPromiseResolutionAsWakeLockSentinel(
+      screen_promise);
+  ASSERT_TRUE(sentinel);
 
   auto* event_listener =
       MakeGarbageCollected<SyncEventListener>(WTF::Bind([]() {