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

Source/platform/heap/ThreadState.cpp

Index: Source/platform/heap/ThreadState.cpp
diff --git a/Source/platform/heap/ThreadState.cpp b/Source/platform/heap/ThreadState.cpp
index 581aee1e7d67f5ce58f9d21cf8f695c6468224eb..63a9c5058b2d1e13bb9808a221bf7e0e76bf0f2c 100644
--- a/Source/platform/heap/ThreadState.cpp
+++ b/Source/platform/heap/ThreadState.cpp
@@ -446,7 +446,7 @@
     shutdownHeapIfNecessary();
 }
 
-void ThreadState::visitPersistentRoots(Visitor* visitor)
+void ThreadState::visitRoots(Visitor* visitor)
 {
     {
         // All threads are at safepoints so this is not strictly necessary.
@@ -458,14 +458,17 @@
 
     AttachedThreadStateSet& threads = attachedThreads();
     for (AttachedThreadStateSet::iterator it = threads.begin(), end = threads.end(); it != end; ++it)
-        (*it)->visitPersistents(visitor);
-}
-
-void ThreadState::visitStackRoots(Visitor* visitor)
-{
-    AttachedThreadStateSet& threads = attachedThreads();
-    for (AttachedThreadStateSet::iterator it = threads.begin(), end = threads.end(); it != end; ++it)
-        (*it)->visitStack(visitor);
+        (*it)->trace(visitor);
+}
+
+void ThreadState::visitLocalRoots(Visitor* visitor)
+{
+    // We assume that orphaned pages have no objects reachable from persistent
+    // handles on other threads or CrossThreadPersistents. The only cases where
+    // this could happen is if a global conservative GC finds a "pointer" on
+    // the stack or due to a programming error where an object has a dangling
+    // cross-thread pointer to an object on this heap.
+    m_persistents->trace(visitor);
 }
 
 NO_SANITIZE_ADDRESS
@@ -499,9 +502,6 @@
 NO_SANITIZE_ADDRESS
 void ThreadState::visitStack(Visitor* visitor)
 {
-    if (m_stackState == NoHeapPointersOnStack)
-        return;
-
     Address* start = reinterpret_cast<Address*>(m_startOfStack);
     // If there is a safepoint scope marker we should stop the stack
     // scanning there to not touch active parts of the stack. Anything
@@ -544,6 +544,13 @@
 void ThreadState::visitPersistents(Visitor* visitor)
 {
     m_persistents->trace(visitor);
+}
+
+void ThreadState::trace(Visitor* visitor)
+{
+    if (m_stackState == HeapPointersOnStack)
+        visitStack(visitor);
+    visitPersistents(visitor);
 }
 
 bool ThreadState::checkAndMarkPointer(Visitor* visitor, Address address)