Bug 1087330. Make the data structure we use for our promise microtask queue have O(1) first element removal, not O(N). r=khuey

dom/promise/Promise.cpp

@@ -482,10 +482,10 @@ bool
 Promise::PerformMicroTaskCheckpoint()
 {
   CycleCollectedJSRuntime* runtime = CycleCollectedJSRuntime::Get();
-  nsTArray<nsCOMPtr<nsIRunnable>>& microtaskQueue =
+  std::queue<nsCOMPtr<nsIRunnable>>& microtaskQueue =
     runtime->GetPromiseMicroTaskQueue();
 
-  if (microtaskQueue.IsEmpty()) {
+  if (microtaskQueue.empty()) {
     return false;
   }
 
@@ -495,11 +495,11 @@ Promise::PerformMicroTaskCheckpoint()
   }
 
   do {
-    nsCOMPtr<nsIRunnable> runnable = microtaskQueue.ElementAt(0);
+    nsCOMPtr<nsIRunnable> runnable = microtaskQueue.front();
     MOZ_ASSERT(runnable);
 
     // This function can re-enter, so we remove the element before calling.
-    microtaskQueue.RemoveElementAt(0);
+    microtaskQueue.pop();
     nsresult rv = runnable->Run();
     if (NS_WARN_IF(NS_FAILED(rv))) {
       return false;
@@ -507,7 +507,7 @@ Promise::PerformMicroTaskCheckpoint()
     if (cx.isSome()) {
       JS_CheckForInterrupt(cx.ref());
     }
-  } while (!microtaskQueue.IsEmpty());
+  } while (!microtaskQueue.empty());
 
   return true;
 }
@@ -1168,10 +1168,10 @@ Promise::DispatchToMicroTask(nsIRunnable* aRunnable)
   MOZ_ASSERT(aRunnable);
 
   CycleCollectedJSRuntime* runtime = CycleCollectedJSRuntime::Get();
-  nsTArray<nsCOMPtr<nsIRunnable>>& microtaskQueue =
+  std::queue<nsCOMPtr<nsIRunnable>>& microtaskQueue =
     runtime->GetPromiseMicroTaskQueue();
 
-  microtaskQueue.AppendElement(aRunnable);
+  microtaskQueue.push(aRunnable);
 }
 
 #if defined(DOM_PROMISE_DEPRECATED_REPORTING)

xpcom/base/CycleCollectedJSRuntime.cpp

@@ -961,7 +961,7 @@ CycleCollectedJSRuntime::SetPendingException(nsIException* aException)
   mPendingException = aException;
 }
 
-nsTArray<nsCOMPtr<nsIRunnable>>&
+std::queue<nsCOMPtr<nsIRunnable>>&
 CycleCollectedJSRuntime::GetPromiseMicroTaskQueue()
 {
   return mPromiseMicroTaskQueue;

xpcom/base/CycleCollectedJSRuntime.h

@@ -7,6 +7,8 @@
 #ifndef mozilla_CycleCollectedJSRuntime_h__
 #define mozilla_CycleCollectedJSRuntime_h__
 
+#include <queue>
+
 #include "mozilla/DeferredFinalize.h"
 #include "mozilla/MemoryReporting.h"
 #include "jsapi.h"
@@ -261,7 +263,7 @@ public:
   already_AddRefed<nsIException> GetPendingException() const;
   void SetPendingException(nsIException* aException);
 
-  nsTArray<nsCOMPtr<nsIRunnable>>& GetPromiseMicroTaskQueue();
+  std::queue<nsCOMPtr<nsIRunnable>>& GetPromiseMicroTaskQueue();
 
   nsCycleCollectionParticipant* GCThingParticipant();
   nsCycleCollectionParticipant* ZoneParticipant();
@@ -322,7 +324,7 @@ private:
 
   nsCOMPtr<nsIException> mPendingException;
 
-  nsTArray<nsCOMPtr<nsIRunnable>> mPromiseMicroTaskQueue;
+  std::queue<nsCOMPtr<nsIRunnable>> mPromiseMicroTaskQueue;
 
   OOMState mOutOfMemoryState;
   OOMState mLargeAllocationFailureState;