3 files changed, 63 insertions, 1 deletions
diff --git a/xpcom/base/CycleCollectedJSContext.cpp b/xpcom/base/CycleCollectedJSContext.cpp
index e16c15455..0a85ae6ac 100644
--- a/xpcom/base/CycleCollectedJSContext.cpp
+++ b/xpcom/base/CycleCollectedJSContext.cpp
@@ -79,6 +79,7 @@
 #include "nsCycleCollectionParticipant.h"
 #include "nsCycleCollector.h"
 #include "nsDOMJSUtils.h"
+#include "nsDOMMutationObserver.h"
 #include "nsJSUtils.h"
 #include "nsWrapperCache.h"
 
@@ -438,6 +439,7 @@ CycleCollectedJSContext::CycleCollectedJSContext()
   , mJSHolders(256)
   , mDoingStableStates(false)
   , mDisableMicroTaskCheckpoint(false)
+  , mMicroTaskLevel(0)
   , mOutOfMemoryState(OOMState::OK)
   , mLargeAllocationFailureState(OOMState::OK)
 {
@@ -1379,7 +1381,7 @@ CycleCollectedJSContext::AfterProcessTask(uint32_t aRecursionDepth)
   // Step 4.1: Execute microtasks.
   if (!mDisableMicroTaskCheckpoint) {
     if (NS_IsMainThread()) {
-      nsContentUtils::PerformMainThreadMicroTaskCheckpoint();
+      PerformMainThreadMicroTaskCheckpoint();
       Promise::PerformMicroTaskCheckpoint();
     } else {
       Promise::PerformWorkerMicroTaskCheckpoint();
@@ -1660,6 +1662,14 @@ CycleCollectedJSContext::DispatchToMicroTask(already_AddRefed<nsIRunnable> aRunn
 }
 
 void
+CycleCollectedJSContext::PerformMainThreadMicroTaskCheckpoint()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
+  nsDOMMutationObserver::HandleMutations();
+}
+
+void
 CycleCollectedJSContext::EnvironmentPreparer::invoke(JS::HandleObject scope,
                                                      js::ScriptEnvironmentPreparer::Closure& closure)
 {
diff --git a/xpcom/base/CycleCollectedJSContext.h b/xpcom/base/CycleCollectedJSContext.h
index ac4cf4361..2197eae92 100644
--- a/xpcom/base/CycleCollectedJSContext.h
+++ b/xpcom/base/CycleCollectedJSContext.h
@@ -402,6 +402,37 @@ public:
   // Queue an async microtask to the current main or worker thread.
   virtual void DispatchToMicroTask(already_AddRefed<nsIRunnable> aRunnable);
 
+  // Call EnterMicroTask when you're entering JS execution.
+  // Usually the best way to do this is to use nsAutoMicroTask.
+  void EnterMicroTask()
+  {
+    ++mMicroTaskLevel;
+  }
+
+  void LeaveMicroTask()
+  {
+    if (--mMicroTaskLevel == 0) {
+      PerformMainThreadMicroTaskCheckpoint();
+    }
+  }
+
+  bool IsInMicroTask()
+  {
+    return mMicroTaskLevel != 0;
+  }
+
+  uint32_t MicroTaskLevel()
+  {
+    return mMicroTaskLevel;
+  }
+
+  void SetMicroTaskLevel(uint32_t aLevel)
+  {
+    mMicroTaskLevel = aLevel;
+  }
+
+  void PerformMainThreadMicroTaskCheckpoint();
+
   // Storage for watching rejected promises waiting for some client to
   // consume their rejection.
 
@@ -452,6 +483,7 @@ private:
 
   bool mDisableMicroTaskCheckpoint;
 
+  uint32_t mMicroTaskLevel;
   OOMState mOutOfMemoryState;
   OOMState mLargeAllocationFailureState;
 
@@ -470,6 +502,25 @@ private:
   EnvironmentPreparer mEnvironmentPreparer;
 };
 
+class MOZ_STACK_CLASS nsAutoMicroTask
+{
+public:
+  nsAutoMicroTask()
+  {
+    CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
+    if (ccjs) {
+      ccjs->EnterMicroTask();
+    }
+  }
+  ~nsAutoMicroTask()
+  {
+    CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
+    if (ccjs) {
+      ccjs->LeaveMicroTask();
+    }
+  }
+};
+
 void TraceScriptHolder(nsISupports* aHolder, JSTracer* aTracer);
 
 // Returns true if the JS::TraceKind is one the cycle collector cares about.
diff --git a/xpcom/base/moz.build b/xpcom/base/moz.build
index d6a336b40..0fdf47d7d 100644
--- a/xpcom/base/moz.build
+++ b/xpcom/base/moz.build
@@ -152,6 +152,7 @@ FINAL_LIBRARY = 'xul'
 
 LOCAL_INCLUDES += [
     '../build',
+    '/dom/base',
     '/xpcom/ds',
 ]