[DevTools] Make resource tree model optional

third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js

Index: third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js
diff --git a/third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js b/third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js
index 4a2f10217bd766b2a4f6d8d32591b94c5aa0d011..a71a3a36a6dc9c7db684663a7c89954085ea4ab1 100644
--- a/third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js
+++ b/third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js
@@ -32,14 +32,17 @@
  * @constructor
  * @extends {WebInspector.SDKModel}
  * @param {!WebInspector.Target} target
+ * @param {!WebInspector.DOMModel} domModel
+ * @param {!WebInspector.ResourceTreeModel} resourceTreeModel
  */
-WebInspector.CSSModel = function(target)
+WebInspector.CSSModel = function(target, domModel, resourceTreeModel)
 {
     WebInspector.SDKModel.call(this, WebInspector.CSSModel, target);
-    this._domModel = WebInspector.DOMModel.fromTarget(target);
+    this._domModel = domModel;
+    this._resourceTreeModel = resourceTreeModel;
     this._agent = target.cssAgent();
     this._styleLoader = new WebInspector.CSSModel.ComputedStyleLoader(this);
-    target.resourceTreeModel.addEventListener(WebInspector.ResourceTreeModel.EventTypes.MainFrameNavigated, this._mainFrameNavigated, this);
+    resourceTreeModel.addEventListener(WebInspector.ResourceTreeModel.EventTypes.MainFrameNavigated, this._mainFrameNavigated, this);
     target.registerCSSDispatcher(new WebInspector.CSSDispatcher(this));
     this._agent.enable().then(this._wasEnabled.bind(this));
     /** @type {!Map.<string, !WebInspector.CSSStyleSheetHeader>} */
@@ -236,7 +239,15 @@ WebInspector.CSSModel.prototype = {
      */
     domModel: function()
     {
-        return /** @type {!WebInspector.DOMModel} */(this._domModel);
+        return this._domModel;
+    },
+
+    /**
+     * @return {!WebInspector.ResourceTreeModel}
+     */
+    resourceTreeModel: function()
+    {
+        return this._resourceTreeModel;
     },
 
     /**
@@ -727,7 +738,7 @@ WebInspector.CSSModel.prototype = {
      */
     requestViaInspectorStylesheet: function(node, userCallback)
     {
-        var frameId = node.frameId() || this.target().resourceTreeModel.mainFrame.id;
+        var frameId = node.frameId() || this._resourceTreeModel.mainFrame.id;
         var headers = this._styleSheetIdToHeader.valuesArray();
         for (var i = 0; i < headers.length; ++i) {
             var styleSheetHeader = headers[i];