Guard against undefined fields in global context.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index bc7550ed9a63e3a8ff55a6ed815ea4b93d8b9f79..2a3439f306466c6850a98f49cb64b8ff3c1224f9 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -648,7 +648,10 @@ void Heap::ClearJSFunctionResultCaches() {
     // Clear the caches:
     int length = caches->length();
     for (int i = 0; i < length; i++) {
-      JSFunctionResultCache::cast(caches->get(i))->Clear();
+      Object* cache = caches->get(i);
+      if (!cache->IsUndefined()) {
+        JSFunctionResultCache::cast(cache)->Clear();
+      }
     }
     // Get the next context:
     context = Context::cast(context)->get(Context::NEXT_CONTEXT_LINK);
@@ -665,7 +668,11 @@ void Heap::ClearNormalizedMapCaches() {
 
   Object* context = global_contexts_list_;
   while (!context->IsUndefined()) {
-    Context::cast(context)->normalized_map_cache()->Clear();
+    int index = Context::NORMALIZED_MAP_CACHE_INDEX;

[Vyacheslav Egorov (Chromium), 2011/12/13 12:26:20]

I don't think we need separate variable just for index.

[ulan, 2011/12/13 13:02:58]

Done.

+    Object* cache = Context::cast(context)->get(index);
+    if (!cache->IsUndefined()) {

[Vyacheslav Egorov (Chromium), 2011/12/13 12:26:20]

please comment why we need to guard against partial initialized objects.

[ulan, 2011/12/13 13:02:58]

Done.

+      NormalizedMapCache::cast(cache)->Clear();
+    }
     context = Context::cast(context)->get(Context::NEXT_CONTEXT_LINK);
   }
 }