DevTools: fix 'Failed to write into a temp file' when recording a filmstrip

Source/devtools/front_end/sdk/TracingModel.js

Index: Source/devtools/front_end/sdk/TracingModel.js
diff --git a/Source/devtools/front_end/sdk/TracingModel.js b/Source/devtools/front_end/sdk/TracingModel.js
index 5aa30abf199c8827f4b1ad3223c0489b9bf440fe..b102c689dcebfc88798b428caa4a400ac5ca68c1 100644
--- a/Source/devtools/front_end/sdk/TracingModel.js
+++ b/Source/devtools/front_end/sdk/TracingModel.js
@@ -10,8 +10,10 @@
  */
 WebInspector.TracingModel = function(backingStorage)
 {
-    this._backingStorage = backingStorage;
     this.reset();
+    // Set backing storage after reset so that we do not perform
+    // an extra reset of backing storage -- this is not free.
+    this._backingStorage = backingStorage;
 }
 
 /**
@@ -190,7 +192,8 @@ WebInspector.TracingModel.prototype = {
         this._minimumRecordTime = 0;
         this._maximumRecordTime = 0;
         this._devToolsMetadataEvents = [];
-        this._backingStorage.reset();
+        if (this._backingStorage)
+            this._backingStorage.reset();
         this._appendDelimiter = false;
         /** @type {!Array<!WebInspector.TracingModel.Event>} */
         this._asyncEvents = [];