No longer OOM on invalid string length.

src/debug.cc

Index: src/debug.cc
diff --git a/src/debug.cc b/src/debug.cc
index c8a99d51711fa44b3f832e023ef0efc22e27f012..d7667f19c8b2d6ed0a5d7dc3b3705f7a8f37cd13 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -754,6 +754,7 @@ bool Debug::CompileDebuggerScript(Isolate* isolate, int index) {
       isolate->bootstrapper()->NativesSourceLookup(index);
   Vector<const char> name = Natives::GetScriptName(index);
   Handle<String> script_name = factory->NewStringFromAscii(name);
+  ASSERT(!script_name.is_null());
   Handle<Context> context = isolate->native_context();
 
   // Compile the script.
@@ -2599,6 +2600,7 @@ Handle<Object> Debugger::MakeJSObject(Vector<const char> constructor_name,
   // Create the execution state object.
   Handle<String> constructor_str =
       isolate_->factory()->InternalizeUtf8String(constructor_name);
+  ASSERT(!constructor_str.is_null());
   Handle<Object> constructor(
       isolate_->global_object()->GetPropertyNoExceptionThrown(*constructor_str),
       isolate_);