Remove references to isBackground

LayoutTests/http/tests/inspector/timeline-test.js

 var initialize_Timeline = function() {
 
 // Scrub values when printing out these properties in the record or data field.
 InspectorTest.timelinePropertyFormatters = {
     children: "formatAsTypeName",
     endTime: "formatAsTypeName",
     requestId: "formatAsTypeName",
     startTime: "formatAsTypeName",
     stackTrace: "formatAsTypeName",
     url: "formatAsURL",
@@ skipping 267 matching lines @@
 {
     this._delegate = delegate;
     this._callback = callback;
     this._input = input;
     this._loadedSize = 0;
     this._fileSize = input.length;
 };
 
 InspectorTest.dumpFrame = function(frame)
 {
-    var fieldsToDump = ["cpuTime", "duration", "startTime", "endTime", "id", "mainThreadFrameId", "isBackground", "timeByCategory", "other", "scripting", "painting", "rendering", "committedFrom"];
+    var fieldsToDump = ["cpuTime", "duration", "startTime", "endTime", "id", "mainThreadFrameId", "timeByCategory", "other", "scripting", "painting", "rendering", "committedFrom"];
     function formatFields(object)
     {
         var result = {};
         for (var key in object) {
             if (fieldsToDump.indexOf(key) < 0)
                 continue;
             var value = object[key];
             if (typeof value === "number")
                 value = Number(value.toFixed(7));
             else if (typeof value === "object" && value)
@@ skipping 41 matching lines @@
         return this._fileSize;
     },
 
     fileName: function()
     {
         return "fakeFile";
     }
 };
 
 };