Assert external strings in external string table. Remove TODOs.

R=hpayer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/23567002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16440 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap-inl.h

@@ -718,13 +718,11 @@ void ExternalStringTable::Verify() {
 #ifdef DEBUG
   for (int i = 0; i < new_space_strings_.length(); ++i) {
     Object* obj = Object::cast(new_space_strings_[i]);
-    // TODO(yangguo): check that the object is indeed an external string.
     ASSERT(heap_->InNewSpace(obj));
     ASSERT(obj != HEAP->the_hole_value());
   }
   for (int i = 0; i < old_space_strings_.length(); ++i) {
     Object* obj = Object::cast(old_space_strings_[i]);
-    // TODO(yangguo): check that the object is indeed an external string.
     ASSERT(!heap_->InNewSpace(obj));
     ASSERT(obj != HEAP->the_hole_value());
   }

src/heap.cc

@@ -7916,6 +7916,7 @@ void ExternalStringTable::CleanUp() {
     if (new_space_strings_[i] == heap_->the_hole_value()) {
       continue;
     }
+    ASSERT(new_space_strings_[i]->IsExternalString());
     if (heap_->InNewSpace(new_space_strings_[i])) {
       new_space_strings_[last++] = new_space_strings_[i];
     } else {
@@ -7930,6 +7931,7 @@ void ExternalStringTable::CleanUp() {
     if (old_space_strings_[i] == heap_->the_hole_value()) {
       continue;
     }
+    ASSERT(old_space_strings_[i]->IsExternalString());
     ASSERT(!heap_->InNewSpace(old_space_strings_[i]));
     old_space_strings_[last++] = old_space_strings_[i];
   }