ScriptState::contextIsEmpty shouldn't return true for a context whose global object is detached

Source/core/inspector/PageRuntimeAgent.cpp

Index: Source/core/inspector/PageRuntimeAgent.cpp
diff --git a/Source/core/inspector/PageRuntimeAgent.cpp b/Source/core/inspector/PageRuntimeAgent.cpp
index 4885cdf7a1c7117c21af9edc1a92646143acdfaa..5dccc1356e7b9386582bb6e774ff8548bf0d3762 100644
--- a/Source/core/inspector/PageRuntimeAgent.cpp
+++ b/Source/core/inspector/PageRuntimeAgent.cpp
@@ -170,7 +170,7 @@ void PageRuntimeAgent::frameWindowDiscarded(LocalDOMWindow* window)
     Vector<RefPtr<ScriptState> > scriptStatesToRemove;
     for (ScriptStateToId::iterator it = m_scriptStateToId.begin(); it != m_scriptStateToId.end(); ++it) {
         RefPtr<ScriptState> scriptState = it->key;
-        if (scriptState->contextIsEmpty() || window == scriptState->domWindow()) {
+        if (scriptState->contextIsValid() || window == scriptState->domWindow()) {
             scriptStatesToRemove.append(scriptState);
             m_frontend->executionContextDestroyed(it->value);
         }