Reapply: [oilpan]: Change marking to do precise roots first and conservative

Source/platform/heap/ThreadState.h

Index: Source/platform/heap/ThreadState.h
diff --git a/Source/platform/heap/ThreadState.h b/Source/platform/heap/ThreadState.h
index 0ff7243bf3bac5dce6282c018f24d7357f064d55..39df3f485979993816852eca748a5531967f905e 100644
--- a/Source/platform/heap/ThreadState.h
+++ b/Source/platform/heap/ThreadState.h
@@ -242,8 +242,11 @@ public:
     static void attachMainThread();
     static void detachMainThread();
 
-    // Trace all GC roots, called when marking the managed heap objects.
-    static void visitRoots(Visitor*);
+    // Trace all persistent roots, called when marking the managed heap objects.
+    static void visitPersistentRoots(Visitor*);
+
+    // Trace all objects found on the stack, used when doing conservative GCs.
+    static void visitStackRoots(Visitor*);
 
     // Associate ThreadState object with the current thread. After this
     // call thread can start using the garbage collected heap infrastructure.
@@ -509,7 +512,6 @@ public:
     HeapStats& statsAfterLastGC() { return m_statsAfterLastGC; }
 
     void setupHeapsForTermination();
-    void visitLocalRoots(Visitor*);
 
 private:
     explicit ThreadState();
@@ -562,8 +564,6 @@ private:
     // and lazily construct ThreadState in it using placement new.
     static uint8_t s_mainThreadStateStorage[];
 
-    void trace(Visitor*);
-
     ThreadIdentifier m_thread;
     OwnPtr<PersistentNode> m_persistents;
     StackState m_stackState;