Oilpan: Introduce class MainThreadOnly

Source/platform/heap/Heap.cpp

Index: Source/platform/heap/Heap.cpp
diff --git a/Source/platform/heap/Heap.cpp b/Source/platform/heap/Heap.cpp
index fe91e41e8de11f975323192664639643827fc205..52d8a2a927d2fe16f9ab521406e2bb1299d3e234 100644
--- a/Source/platform/heap/Heap.cpp
+++ b/Source/platform/heap/Heap.cpp
@@ -2435,7 +2435,7 @@ void Heap::collectGarbage(ThreadState::StackState stackState, ThreadState::Cause
     // Disallow allocation during garbage collection (but not
     // during the finalization that happens when the gcScope is
     // torn down).
-    NoAllocationScope<AnyThread> noAllocationScope;
+    NoAllocationScope<AnyThreadAffinity> noAllocationScope;
 
     prepareForGC();
 
@@ -2491,7 +2491,7 @@ void Heap::collectGarbageForTerminatingThread(ThreadState* state)
     // same time as a thread local GC.
 
     {
-        NoAllocationScope<AnyThread> noAllocationScope;
+        NoAllocationScope<AnyThreadAffinity> noAllocationScope;
 
         state->enterGC();
         state->prepareForGC();