Fix stack overflow test failures with no snap.

src/debug.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 802 matching lines @@
 
   // Create the debugger context.
   HandleScope scope(isolate_);
   Handle<Context> context =
       isolate_->bootstrapper()->CreateEnvironment(
           isolate_,
           Handle<Object>::null(),
           v8::Handle<ObjectTemplate>(),
           NULL);
 
+  // Fail if no context could be created.
+  if (context.is_null()) return false;
+
   // Use the debugger context.
   SaveContext save(isolate_);
   isolate_->set_context(*context);
 
   // Expose the builtins object in the debugger context.
   Handle<String> key = isolate_->factory()->LookupAsciiSymbol("builtins");
   Handle<GlobalObject> global = Handle<GlobalObject>(context->global());
   RETURN_IF_EMPTY_HANDLE_VALUE(
       isolate_,
       JSReceiver::SetProperty(global, key, Handle<Object>(global->builtins()),
@@ skipping 2746 matching lines @@
     {
       Locker locker;
       Isolate::Current()->debugger()->CallMessageDispatchHandler();
     }
   }
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal