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

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 e216517b19c34c3a55e56ea1cb3e2653b4621247..1d63ae03a8e385f9488fde3945a09f569e285277 100644
--- a/Source/platform/heap/ThreadState.cpp
+++ b/Source/platform/heap/ThreadState.cpp
@@ -447,7 +447,7 @@ void ThreadState::detach()
     shutdownHeapIfNecessary();
 }
 
-void ThreadState::visitRoots(Visitor* visitor)
+void ThreadState::visitPersistentRoots(Visitor* visitor)
 {
     {
         // All threads are at safepoints so this is not strictly necessary.
@@ -459,17 +459,14 @@ void ThreadState::visitRoots(Visitor* visitor)
 
     AttachedThreadStateSet& threads = attachedThreads();
     for (AttachedThreadStateSet::iterator it = threads.begin(), end = threads.end(); it != end; ++it)
-        (*it)->trace(visitor);
+        (*it)->visitPersistents(visitor);
 }
 
-void ThreadState::visitLocalRoots(Visitor* visitor)
+void ThreadState::visitStackRoots(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);
+    AttachedThreadStateSet& threads = attachedThreads();
+    for (AttachedThreadStateSet::iterator it = threads.begin(), end = threads.end(); it != end; ++it)
+        (*it)->visitStack(visitor);
 }
 
 NO_SANITIZE_ADDRESS
@@ -503,6 +500,9 @@ void ThreadState::visitAsanFakeStackForPointer(Visitor* visitor, Address ptr)
 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
@@ -547,13 +547,6 @@ 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)
 {
     // If thread is terminating ignore conservative pointers.