[Devtools] Clear cache before running the test

third_party/WebKit/LayoutTests/http/tests/inspector/network-test.js

 // This goes before everything else to keep console message line number invariant.
 var lastXHRIndex = 0;
 function xhrLoadedCallback()
 {
     // We need to make sure the console message text is unique so that we don't end up with repeat count update only.
     console.log("XHR loaded: " + (++lastXHRIndex));
 }
 
 function makeSimpleXHR(method, url, async, callback)
 {
@@ skipping 106 matching lines @@
 
     InspectorTest.addConsoleSniffer(innerCallback);
     InspectorTest.evaluateInPage("makeXHRForJSONArguments(\"" + jsonArgs + "\")");
 }
 
 InspectorTest.makeFetch = function(url, requestInitializer, callback)
 {
     InspectorTest.callFunctionInPageAsync("makeFetch", [url, requestInitializer]).then(callback);
 }
 
+InspectorTest.clearNetworkCache = function(finishedCallback)
+{
+  // This turns cache off and then on, effectively clearning the cache.
+  var networkAgent = InspectorTest.NetworkAgent;
+  var promise = networkAgent.setCacheDisabled(true);
+  promise.then(networkAgent.setCacheDisabled.bind(networkAgent, false));
+  promise.then(finishedCallback);
+}
+
 InspectorTest.HARPropertyFormatters = {
     bodySize: "formatAsTypeName",
     compression: "formatAsTypeName",
     connection: "formatAsTypeName",
     headers: "formatAsTypeName",
     headersSize: "formatAsTypeName",
     id: "formatAsTypeName",
     onContentLoad: "formatAsTypeName",
     onLoad: "formatAsTypeName",
     receive: "formatAsTypeName",
     startedDateTime: "formatAsRecentTime",
     time: "formatAsTypeName",
     timings: "formatAsTypeName",
     version: "formatAsTypeName",
     wait: "formatAsTypeName",
     _transferSize: "formatAsTypeName",
     _error: "skip"
 };
 // addObject checks own properties only, so make a deep copy rather than use prototype.
 InspectorTest.HARPropertyFormattersWithSize = JSON.parse(JSON.stringify(InspectorTest.HARPropertyFormatters));
 InspectorTest.HARPropertyFormattersWithSize.size = "formatAsTypeName";
 
 };