[debug] Extend a test and fix some typos.

src/debug/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/debug/debug.h"
 
 #include <memory>
 
 #include "src/api.h"
 #include "src/arguments.h"
@@ skipping 1927 matching lines @@
     // Invoke the JavaScript debug event listener.
     DCHECK(event_listener_->IsJSFunction());
     Handle<Object> argv[] = { Handle<Object>(Smi::FromInt(event), isolate_),
                               exec_state,
                               event_data,
                               event_listener_data_ };
     Handle<JSReceiver> global = isolate_->global_proxy();
     MaybeHandle<Object> result =
         Execution::Call(isolate_, Handle<JSFunction>::cast(event_listener_),
                         global, arraysize(argv), argv);
-    CHECK(!result.is_null());  // Listeners may not throw.
+    CHECK(!result.is_null());  // Listeners must not throw.
   }
   in_debug_event_listener_ = previous;
 }
 
 
 void Debug::ProcessCompileEvent(v8::DebugEvent event, Handle<Script> script) {
   if (ignore_events()) return;
   SuppressDebug while_processing(this);
 
   bool in_nested_debug_scope = in_debug_scope();
@@ skipping 687 matching lines @@
 }
 
 
 void LockingCommandMessageQueue::Clear() {
   base::LockGuard<base::Mutex> lock_guard(&mutex_);
   queue_.Clear();
 }
 
 }  // namespace internal
 }  // namespace v8