[DevTools] Make resource tree model optional

third_party/WebKit/Source/devtools/front_end/bindings/StylesSourceMapping.js

Index: third_party/WebKit/Source/devtools/front_end/bindings/StylesSourceMapping.js
diff --git a/third_party/WebKit/Source/devtools/front_end/bindings/StylesSourceMapping.js b/third_party/WebKit/Source/devtools/front_end/bindings/StylesSourceMapping.js
index d02ce0a5f8de7668078bb081ce7cd6fe1b16fb33..be9c89b45875507142cddb0fc86cdab5d89299e6 100644
--- a/third_party/WebKit/Source/devtools/front_end/bindings/StylesSourceMapping.js
+++ b/third_party/WebKit/Source/devtools/front_end/bindings/StylesSourceMapping.js
@@ -44,7 +44,9 @@ WebInspector.StylesSourceMapping = function(cssModel, workspace, networkMapping)
     this._workspace.addEventListener(WebInspector.Workspace.Events.UISourceCodeRemoved, this._uiSourceCodeRemoved, this);
     this._networkMapping = networkMapping;
 
-    cssModel.target().resourceTreeModel.addEventListener(WebInspector.ResourceTreeModel.EventTypes.MainFrameNavigated, this._unbindAllUISourceCodes, this);
+    var resourceTreeModel = WebInspector.ResourceTreeModel.fromTarget(cssModel.target());
+    if (resourceTreeModel)

[pfeldman, 2016/07/07 17:44:14]

We always have resourceTreeModel when we have CSS.

[eostroukhov-old, 2016/07/13 23:30:58]

I added an accessor to get it through the cssModel.

+        resourceTreeModel.addEventListener(WebInspector.ResourceTreeModel.EventTypes.MainFrameNavigated, this._unbindAllUISourceCodes, this);
 
     this._cssModel.addEventListener(WebInspector.CSSModel.Events.StyleSheetChanged, this._styleSheetChanged, this);
     /** @type {!Map<string, !Map<string, !Map<string, !WebInspector.CSSStyleSheetHeader>>>} */