Reset ThreadState weak callback stack before GCing.

third_party/WebKit/Source/platform/heap/CallbackStack.cpp

Index: third_party/WebKit/Source/platform/heap/CallbackStack.cpp
diff --git a/third_party/WebKit/Source/platform/heap/CallbackStack.cpp b/third_party/WebKit/Source/platform/heap/CallbackStack.cpp
index a80bd4e432d597fe58991722ee779b483855882b..7a13b0b32f3a24d94aef0ebf9cbc6767e19d92a7 100644
--- a/third_party/WebKit/Source/platform/heap/CallbackStack.cpp
+++ b/third_party/WebKit/Source/platform/heap/CallbackStack.cpp
@@ -45,11 +45,15 @@ void CallbackStack::Block::clear()
 
 void CallbackStack::Block::decommit()
 {
+    reset();
+    WTF::discardSystemPages(m_buffer, m_blockSize * sizeof(Item));
+}
+
+void CallbackStack::Block::reset()
+{
 #if ENABLE(ASSERT)
     clear();
 #endif
-    WTF::discardSystemPages(m_buffer, m_blockSize * sizeof(Item));
-
     m_current = &m_buffer[0];
     m_next = nullptr;
 }
@@ -90,6 +94,17 @@ CallbackStack::~CallbackStack()
     m_last = nullptr;
 }
 
+void CallbackStack::clear()
+{
+    Block* next;
+    for (Block* current = m_first->next(); current; current = next) {
+        next = current->next();
+        delete current;
+    }
+    m_first->reset();
+    m_last = m_first;
+}
+
 void CallbackStack::decommit()
 {
     Block* next;