Actually fix the memory leak in debugger wrt promises.

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 "v8.h"
 
 #include "api.h"
 #include "arguments.h"
 #include "bootstrapper.h"
 #include "code-stubs.h"
@@ skipping 789 matching lines @@
 
   debug_context_ = Handle<Context>::cast(
       isolate_->global_handles()->Create(*context));
   return true;
 }
 
 
 void Debug::Unload() {
   ClearAllBreakPoints();
 
+  // Match unmatched PromiseHandlePrologue calls.
+  while (thread_local_.promise_on_stack_) PromiseHandleEpilogue();
+
   // Return debugger is not loaded.
   if (!IsLoaded()) return;
 
   // Clear the script cache.
   DestroyScriptCache();
 
-  // Match unmatched PromiseHandlePrologue calls.
-  while (thread_local_.promise_on_stack_) PromiseHandleEpilogue();
-
   // Clear debugger context global handle.
   GlobalHandles::Destroy(Handle<Object>::cast(debug_context_).location());
   debug_context_ = Handle<Context>();
 }
 
 
 Object* Debug::Break(Arguments args) {
   Heap* heap = isolate_->heap();
   HandleScope scope(isolate_);
   ASSERT(args.length() == 0);
@@ skipping 2714 matching lines @@
   logger_->DebugEvent("Put", message.text());
 }
 
 
 void LockingCommandMessageQueue::Clear() {
   LockGuard<Mutex> lock_guard(&mutex_);
   queue_.Clear();
 }
 
 } }  // namespace v8::internal