Make check in GetExternalString a runtime check instead of ASSERT....

src/api.cc

 // Copyright 2009 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 2337 matching lines @@
   EnsureInitialized("v8::String::IsExternalAscii()");
   i::Handle<i::String> str = Utils::OpenHandle(this);
   return i::StringShape(*str).IsExternalAscii();
 }
 
 
 v8::String::ExternalStringResource*
 v8::String::GetExternalStringResource() const {
   EnsureInitialized("v8::String::GetExternalStringResource()");
   i::Handle<i::String> str = Utils::OpenHandle(this);
-  ASSERT(str->IsExternalTwoByteString());
-  void* resource = i::Handle<i::ExternalTwoByteString>::cast(str)->resource();
-  return reinterpret_cast<ExternalStringResource*>(resource);
+  if (i::StringShape(*str).IsExternalTwoByte()) {
+    void* resource = i::Handle<i::ExternalTwoByteString>::cast(str)->resource();
+    return reinterpret_cast<ExternalStringResource*>(resource);
+  } else {
+    return NULL;
+  }
 }
 
 
 v8::String::ExternalAsciiStringResource*
       v8::String::GetExternalAsciiStringResource() const {
   EnsureInitialized("v8::String::GetExternalAsciiStringResource()");
   i::Handle<i::String> str = Utils::OpenHandle(this);
-  ASSERT(str->IsExternalAsciiString());
-  void* resource = i::Handle<i::ExternalAsciiString>::cast(str)->resource();
-  return reinterpret_cast<ExternalAsciiStringResource*>(resource);
+  if (i::StringShape(*str).IsExternalAscii()) {
+    void* resource = i::Handle<i::ExternalAsciiString>::cast(str)->resource();
+    return reinterpret_cast<ExternalAsciiStringResource*>(resource);
+  } else {
+    return NULL;
+  }
 }
 
 
 double Number::Value() const {
   if (IsDeadCheck("v8::Number::Value()")) return 0;
   i::Handle<i::Object> obj = Utils::OpenHandle(this);
   return obj->Number();
 }
 
 
@@ skipping 1081 matching lines @@
       reinterpret_cast<HandleScopeImplementer*>(storage);
   List<void**>* blocks_of_archived_thread = thread_local->Blocks();
   v8::ImplementationUtilities::HandleScopeData* handle_data_of_archived_thread =
       &thread_local->handle_scope_data_;
   Iterate(v, blocks_of_archived_thread, handle_data_of_archived_thread);
 
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal