cc: Add cancel functionality to unique notifier.

This patch adds a Cancel function to UniqueNotifier that can be used
to cancel a task. Currently the only way to get this behavior is to
destroy the UniqueNotifier.

R=enne
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1218173007

Cr-Commit-Position: refs/heads/master@{#337120}

3 files changed, 25 insertions, 1 deletions

diff --git a/cc/base/unique_notifier.cc b/cc/base/unique_notifier.cc
index 0656c6d..eb0b09a 100644
--- a/cc/base/unique_notifier.cc
+++ b/cc/base/unique_notifier.cc
@@ -22,6 +22,10 @@ UniqueNotifier::UniqueNotifier(base::SequencedTaskRunner* task_runner,
 UniqueNotifier::~UniqueNotifier() {
 }
 
+void UniqueNotifier::Cancel() {
+  notification_pending_ = false;
+}
+
 void UniqueNotifier::Schedule() {
   if (notification_pending_)
     return;
@@ -33,6 +37,9 @@ void UniqueNotifier::Schedule() {
 }
 
 void UniqueNotifier::Notify() {
+  if (!notification_pending_)
+    return;
+
   // Note that the order here is important in case closure schedules another
   // run.
   notification_pending_ = false;
diff --git a/cc/base/unique_notifier.h b/cc/base/unique_notifier.h
index 9a4a02c..3cbc22a 100644
--- a/cc/base/unique_notifier.h
+++ b/cc/base/unique_notifier.h
@@ -29,6 +29,9 @@ class CC_EXPORT UniqueNotifier {
   // pending, then only one notification will take place.
   void Schedule();
 
+  // Cancel a pending notification, if one was scheduled.
+  void Cancel();
+
  private:
   void Notify();
 
diff --git a/cc/base/unique_notifier_unittest.cc b/cc/base/unique_notifier_unittest.cc
index 7b52512..b53b52a 100644
--- a/cc/base/unique_notifier_unittest.cc
+++ b/cc/base/unique_notifier_unittest.cc
@@ -50,12 +50,26 @@ TEST_F(UniqueNotifierTest, Schedule) {
     base::RunLoop().RunUntilIdle();
     EXPECT_EQ(2, NotificationCount());
 
+    // Schedule and cancel.
+    notifier.Schedule();
+    notifier.Cancel();
+
+    base::RunLoop().RunUntilIdle();
+    EXPECT_EQ(2, NotificationCount());
+
+    notifier.Schedule();
+    notifier.Cancel();
+    notifier.Schedule();
+
+    base::RunLoop().RunUntilIdle();
+    EXPECT_EQ(3, NotificationCount());
+
     notifier.Schedule();
   }
 
   // Notifier went out of scope, so we don't expect to get a notification.
   base::RunLoop().RunUntilIdle();
-  EXPECT_EQ(2, NotificationCount());
+  EXPECT_EQ(3, NotificationCount());
 }
 
 }  // namespace