Oilpan: We need to collect all garbage before shutting down the worker thread

Source/heap/ThreadState.cpp

Index: Source/heap/ThreadState.cpp
diff --git a/Source/heap/ThreadState.cpp b/Source/heap/ThreadState.cpp
index 233a979afe7ea6e39a9d325529717307e42d90a9..58735a1bf4dd93a325bc49d13003e306ae05f926 100644
--- a/Source/heap/ThreadState.cpp
+++ b/Source/heap/ThreadState.cpp
@@ -296,13 +296,7 @@ void ThreadState::cleanup()
     // After this GC we expect heap to be empty because
     // preCleanup tasks should have cleared all persistent
     // handles that were externally owned.
-    // FIXME: oilpan: we should perform a single GC and everything
-    // should die. Unfortunately it is not the case for all objects
-    // because the hierarchy was not completely moved to the heap and
-    // some heap allocated objects own objects that contain persistents
-    // pointing to other heap allocated objects.
-    Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
-    Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
+    Heap::collectAllGarbage(ThreadState::NoHeapPointersOnStack);
 
     // Verify that all heaps are empty now.
     for (int i = 0; i < NumberOfHeaps; i++)
@@ -317,6 +311,8 @@ void ThreadState::cleanup()
 void ThreadState::detach()
 {
     ThreadState* state = current();
+    state->cleanup();
+
     // Enter safe point before trying to acquire threadAttachMutex
     // to avoid dead lock if another thread is preparing for GC, has acquired
     // threadAttachMutex and waiting for other threads to pause or reach a