[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 1aa6c22a49eed2bb935fcbb51d62600867150590..f82a434634b0bdf0f46b2dad0fe36fdb2d888500 100644
--- a/Source/platform/heap/ThreadState.h
+++ b/Source/platform/heap/ThreadState.h
@@ -245,8 +245,11 @@ 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.
@@ -510,7 +513,6 @@ public:
     HeapStats& statsAfterLastGC() { return m_statsAfterLastGC; }
 
     void setupHeapsForTermination();
-    void visitLocalRoots(Visitor*);
 
 private:
     explicit ThreadState();
@@ -561,8 +563,6 @@ 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;