Add diagnostic message if external blob files cannot be loaded.

src/snapshot/natives-external.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/snapshot/natives.h"
 
 #include "src/base/logging.h"
 #include "src/list.h"
 #include "src/list-inl.h"
 #include "src/snapshot/snapshot-source-sink.h"
@@ skipping 101 matching lines @@
   int debugger_count_;
 
   DISALLOW_COPY_AND_ASSIGN(NativesStore);
 };
 
 
 template<NativeType type>
 class NativesHolder {
  public:
   static NativesStore* get() {
-    DCHECK(holder_);
+    CHECK(holder_);
     return holder_;
   }
   static void set(NativesStore* store) {
-    DCHECK(store);
+    CHECK(store);
     holder_ = store;
   }
   static bool empty() { return holder_ == NULL; }
   static void Dispose() {
     delete holder_;
     holder_ = NULL;
   }
 
  private:
   static NativesStore* holder_;
@@ skipping 96 matching lines @@
   template Vector<const char> NativesCollection<T>::GetScriptName(int i);   \
   template Vector<const char> NativesCollection<T>::GetScriptsSource();
 INSTANTIATE_TEMPLATES(CORE)
 INSTANTIATE_TEMPLATES(EXPERIMENTAL)
 INSTANTIATE_TEMPLATES(EXTRAS)
 INSTANTIATE_TEMPLATES(EXPERIMENTAL_EXTRAS)
 #undef INSTANTIATE_TEMPLATES
 
 }  // namespace internal
 }  // namespace v8