Fix edge case of extension with NULL as source string.

src/api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 523 matching lines @@
                      int dep_count,
                      const char** deps,
                      int source_length)
     : name_(name),
       source_length_(source_length >= 0 ?
                      source_length :
                      (source ? static_cast<int>(strlen(source)) : 0)),
       source_(source, source_length_),
       dep_count_(dep_count),
       deps_(deps),
-      auto_enable_(false) { }
+      auto_enable_(false) {
+  CHECK(source != NULL || source_length_ == 0);
+}
 
 
 v8::Handle<Primitive> Undefined() {
   i::Isolate* isolate = i::Isolate::Current();
   if (!EnsureInitializedForIsolate(isolate, "v8::Undefined()")) {
     return v8::Handle<v8::Primitive>();
   }
   return v8::Handle<Primitive>(ToApi<Primitive>(
       isolate->factory()->undefined_value()));
 }
@@ skipping 5997 matching lines @@
 
   v->VisitPointers(blocks_.first(), first_block_limit_);
 
   for (int i = 1; i < blocks_.length(); i++) {
     v->VisitPointers(blocks_[i], &blocks_[i][kHandleBlockSize]);
   }
 }
 
 
 } }  // namespace v8::internal