Revert of [oilpan]: Change marking to do precise roots first and conservative second.

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 f82a434634b0bdf0f46b2dad0fe36fdb2d888500..1aa6c22a49eed2bb935fcbb51d62600867150590 100644
--- a/Source/platform/heap/ThreadState.h
+++ b/Source/platform/heap/ThreadState.h
@@ -245,11 +245,8 @@
     static void attachMainThread();
     static void detachMainThread();
 
-    // 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*);
+    // Trace all GC roots, called when marking the managed heap objects.
+    static void visitRoots(Visitor*);
 
     // Associate ThreadState object with the current thread. After this
     // call thread can start using the garbage collected heap infrastructure.
@@ -513,6 +510,7 @@
     HeapStats& statsAfterLastGC() { return m_statsAfterLastGC; }
 
     void setupHeapsForTermination();
+    void visitLocalRoots(Visitor*);
 
 private:
     explicit ThreadState();
@@ -562,6 +560,8 @@
     // For this we reserve static storage for the main ThreadState
     // and lazily construct ThreadState in it using placement new.
     static uint8_t s_mainThreadStateStorage[];
+
+    void trace(Visitor*);
 
     ThreadIdentifier m_thread;
     OwnPtr<PersistentNode> m_persistents;