Bug 1515216, ensure IdleTaskRunners are added only once to RefreshDriver's idle runnable list, r=mccr8

Differential Revision: https://phabricator.services.mozilla.com/D27424

--HG--
extra : moz-landing-system : lando

layout/base/nsRefreshDriver.cpp

@@ -1713,10 +1713,16 @@ struct RunnableWithDelay {
 
 static AutoTArray<RunnableWithDelay, 8>* sPendingIdleRunnables = nullptr;
 
-void nsRefreshDriver::DispatchIdleRunnableAfterTick(nsIRunnable* aRunnable,
-                                                    uint32_t aDelay) {
+void nsRefreshDriver::DispatchIdleRunnableAfterTickUnlessExists(
+    nsIRunnable* aRunnable, uint32_t aDelay) {
   if (!sPendingIdleRunnables) {
     sPendingIdleRunnables = new AutoTArray<RunnableWithDelay, 8>();
+  } else {
+    for (uint32_t i = 0; i < sPendingIdleRunnables->Length(); ++i) {
+      if ((*sPendingIdleRunnables)[i].mRunnable == aRunnable) {
+        return;
+      }
+    }
   }
 
   RunnableWithDelay rwd = {aRunnable, aDelay};

layout/base/nsRefreshDriver.h

@@ -415,8 +415,8 @@ class nsRefreshDriver final : public mozilla::layers::TransactionIdAllocator,
    */
   static mozilla::Maybe<mozilla::TimeStamp> GetNextTickHint();
 
-  static void DispatchIdleRunnableAfterTick(nsIRunnable* aRunnable,
-                                            uint32_t aDelay);
+  static void DispatchIdleRunnableAfterTickUnlessExists(nsIRunnable* aRunnable,
+                                                        uint32_t aDelay);
   static void CancelIdleRunnable(nsIRunnable* aRunnable);
 
   void NotifyDOMContentLoaded();

xpcom/threads/IdleTaskRunner.cpp

@@ -119,7 +119,7 @@ void IdleTaskRunner::Schedule(bool aAllowIdleDispatch) {
   TimeStamp hint = nsRefreshDriver::GetIdleDeadlineHint(now);
   if (hint != now) {
     // RefreshDriver is ticking, let it schedule the idle dispatch.
-    nsRefreshDriver::DispatchIdleRunnableAfterTick(this, mDelay);
+    nsRefreshDriver::DispatchIdleRunnableAfterTickUnlessExists(this, mDelay);
     // Ensure we get called at some point, even if RefreshDriver is stopped.
     SetTimerInternal(mDelay);
   } else {