Link all global contexts into a weak list.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index f63d6725ec2981afdf13b294c8a7de8a76d51f31..e48f7854a067434799a0b52c6ca7f79e148107ac 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1485,6 +1485,15 @@ void FixedArray::set_unchecked(int index, Smi* value) {
 }
 
 
+void FixedArray::set_unchecked(int index,
+                               Object* value,
+                               WriteBarrierMode mode) {
+  int offset = kHeaderSize + index * kPointerSize;
+  WRITE_FIELD(this, offset, value);
+  CONDITIONAL_WRITE_BARRIER(this, offset, mode);
+}
+
+
 void FixedArray::set_null_unchecked(int index) {
   ASSERT(index >= 0 && index < this->length());
   ASSERT(!Heap::InNewSpace(Heap::null_value()));