DevTools: disable CSS agent on disconnect.

BUG=358534
R=apavlov@chromium.org

Review URL: https://codereview.chromium.org/221033003

git-svn-id: svn://svn.chromium.org/blink/trunk@170577 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/inspector/InspectorCSSAgent.cpp

@@ -411,6 +411,8 @@ void InspectorCSSAgent::setFrontend(InspectorFrontend* frontend)
 void InspectorCSSAgent::clearFrontend()
 {
     ASSERT(m_frontend);
+    ErrorString error;
+    disable(&error);
     m_frontend = 0;
     resetNonPersistentData();
 }
@@ -507,6 +509,7 @@ void InspectorCSSAgent::wasEnabled(PassRefPtr<EnableCallback> callback)
 
 void InspectorCSSAgent::disable(ErrorString*)
 {
+    reset();
     m_instrumentingAgents->setInspectorCSSAgent(0);
     m_state->setBoolean(CSSAgentState::cssAgentEnabled, false);
 }

third_party/WebKit/Source/devtools/front_end/CSSStyleModel.js

@@ -459,6 +459,8 @@ WebInspector.CSSStyleModel.prototype = {
     {
         var header = this._styleSheetIdToHeader[id];
         console.assert(header);
+        if (!header)
+            return;
         delete this._styleSheetIdToHeader[id];
         var url = header.resourceURL();
         var frameIdToStyleSheetIds = this._styleSheetIdsForURL[url];