Allow collection of DOM objects in minor GC cycles.

src/global-handles.cc

Index: src/global-handles.cc
diff --git a/src/global-handles.cc b/src/global-handles.cc
index c09ba4b476b97e8fc524bc4180c8017d72814167..59af2381dc5249c7d9678293c6e2ef63527c1007 100644
--- a/src/global-handles.cc
+++ b/src/global-handles.cc
@@ -154,6 +154,14 @@ class GlobalHandles::Node {
   }
   bool is_independent() const { return independent_; }
 
+  void MarkExternallyUnreachable(GlobalHandles* global_handles) {
+    ASSERT(state_ != FREE);
+    if (global_handles->isolate()->heap()->InNewSpace(object_))
+      externally_unreachable_ = true;
+  }
+  bool is_externally_unreachable() const { return externally_unreachable_; }
+  bool clear_externally_unreachable() { externally_unreachable_ = false; }
+
   // In-new-space-list flag accessors.
   void set_in_new_space_list(bool v) { in_new_space_list_ = v; }
   bool is_in_new_space_list() const { return in_new_space_list_; }
@@ -260,6 +268,7 @@ class GlobalHandles::Node {
   State state_ : 4;
 
   bool independent_ : 1;
+  bool externally_unreachable_ : 1;
   bool in_new_space_list_ : 1;
 
   // Handle specific callback.
@@ -448,6 +457,11 @@ void GlobalHandles::MarkIndependent(Object** location) {
 }
 
 
+void GlobalHandles::MarkExternallyUnreachable(Object** location) {
+  Node::FromLocation(location)->MarkExternallyUnreachable(this);
+}
+
+
 bool GlobalHandles::IsIndependent(Object** location) {
   return Node::FromLocation(location)->is_independent();
 }
@@ -501,8 +515,9 @@ void GlobalHandles::IterateNewSpaceStrongAndDependentRoots(ObjectVisitor* v) {
   for (int i = 0; i < new_space_nodes_.length(); ++i) {
     Node* node = new_space_nodes_[i];
     if (node->IsStrongRetainer() ||
-        (node->IsWeakRetainer() && !node->is_independent())) {
-      v->VisitPointer(node->location());
+        (node->IsWeakRetainer() && !node->is_independent() &&
+         !node->is_externally_unreachable())) {
+        v->VisitPointer(node->location());
     }
   }
 }
@@ -513,8 +528,8 @@ void GlobalHandles::IdentifyNewSpaceWeakIndependentHandles(
   for (int i = 0; i < new_space_nodes_.length(); ++i) {
     Node* node = new_space_nodes_[i];
     ASSERT(node->is_in_new_space_list());
-    if (node->is_independent() && node->IsWeak() &&
-        f(isolate_->heap(), node->location())) {
+    if ((node->is_independent() || node->is_externally_unreachable()) &&
+        node->IsWeak() && f(isolate_->heap(), node->location())) {
       node->MarkPending();
     }
   }
@@ -525,7 +540,8 @@ void GlobalHandles::IterateNewSpaceWeakIndependentRoots(ObjectVisitor* v) {
   for (int i = 0; i < new_space_nodes_.length(); ++i) {
     Node* node = new_space_nodes_[i];
     ASSERT(node->is_in_new_space_list());
-    if (node->is_independent() && node->IsWeakRetainer()) {
+    if ((node->is_independent() || node->is_externally_unreachable()) &&
+        node->IsWeakRetainer()) {
       v->VisitPointer(node->location());
     }
   }
@@ -547,7 +563,8 @@ bool GlobalHandles::PostGarbageCollectionProcessing(
       // Skip dependent handles. Their weak callbacks might expect to be
       // called between two global garbage collection callbacks which
       // are not called for minor collections.
-      if (!node->is_independent()) continue;
+      if (!node->is_independent() && !node->is_externally_unreachable()) continue;
+      node->clear_externally_unreachable();
       if (node->PostGarbageCollectionProcessing(isolate_, this)) {
         if (initial_post_gc_processing_count != post_gc_processing_count_) {
           // Weak callback triggered another GC and another round of
@@ -563,6 +580,7 @@ bool GlobalHandles::PostGarbageCollectionProcessing(
     }
   } else {
     for (NodeIterator it(this); !it.done(); it.Advance()) {
+      it.node()->clear_externally_unreachable();
       if (it.node()->PostGarbageCollectionProcessing(isolate_, this)) {
         if (initial_post_gc_processing_count != post_gc_processing_count_) {
           // See the comment above.