A couple of other "stack overflow" vs. "has_pending_exception()" issues fixed.

src/debug.cc

 // Copyright 2012 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/v8.h"
 
 #include "src/api.h"
 #include "src/arguments.h"
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
@@ skipping 619 matching lines @@
     MessageLocation computed_location;
     isolate->ComputeLocation(&computed_location);
     Handle<JSMessageObject> message = MessageHandler::MakeMessageObject(
         isolate, MessageTemplate::kDebuggerLoading, &computed_location,
         isolate->factory()->undefined_value(), Handle<JSArray>());
     DCHECK(!isolate->has_pending_exception());
     Handle<Object> exception;
     if (maybe_exception.ToHandle(&exception)) {
       isolate->set_pending_exception(*exception);
       MessageHandler::ReportMessage(isolate, NULL, message);
-      isolate->clear_pending_exception();
     }
+    DCHECK(!maybe_exception.is_null());
     return false;
   }
 
   // Mark this script as native and return successfully.
   Handle<Script> script(Script::cast(function->shared()->script()));
   script->set_type(Smi::FromInt(Script::TYPE_NATIVE));
   return true;
 }
 
 
@@ skipping 2712 matching lines @@
 }
 
 
 void LockingCommandMessageQueue::Clear() {
   base::LockGuard<base::Mutex> lock_guard(&mutex_);
   queue_.Clear();
 }
 
 }  // namespace internal
 }  // namespace v8