[ServiceWorker] Make fetch() method better conformance with the spec.

LayoutTests/http/tests/serviceworker/resources/fetch-access-control-worker.js

+var port = undefined;
+var isTestTargetFetch = false;
+
+self.onmessage = function(e) {
+  var message = e.data;
+  if ('port' in message) {
+    port = message.port;
+  } else if (message.msg === 'START TEST CASE') {
+    isTestTargetFetch = true;
+    port.postMessage({msg: 'READY'});
+  }
+};
+
+function getQueryParams(url) {
+  var search = (new URL(url)).search;
+  if (!search) {
+    return {};
+  }
+  var ret = {};
+  var params = search.substring(1).split('&');
+  params.forEach(function(param) {
+      var element = param.split('=');
+      ret[decodeURIComponent(element[0])] = decodeURIComponent(element[1]);
+    });
+  return ret;
+}
+
+function getRequestInit(params) {
+  var init = {};
+  if (params['method']) {
+    init['method'] = params['method'];
+  }
+  if (params['mode']) {
+    init['mode'] = params['mode'];
+  }
+  if (params['credentials']) {
+    init['credentials'] = params['credentials'];
+  }
+  if (params['headers'] === 'CUSTOM') {
+    init['headers'] = {"X-ServiceWorker-Test": "test"};
+  } else if (params['headers'] === '{}') {
+    init['headers'] = {};
+  }
+  return init;
+}
+
+function headersToArray(headers) {
+  var ret = [];
+  headers.forEach(function(value, key) {
+      ret.push([key, value]);
+    });
+  return ret;
+}
+
+self.addEventListener('fetch', function(event) {
+    var originalURL = event.request.url;
+    if (!isTestTargetFetch) {
+      // Don't handle the event when it is not the test target fetch such as a
+      // redirected fetch or for the iframe html.
+      return;
+    }
+    isTestTargetFetch = false;
+    var params = getQueryParams(originalURL);
+    var init = getRequestInit(params);
+    var url = params['url'];
+    if (params['ignore']) {
+      port.postMessage({fetchResult: 'ignored'});
+      return;
+    }
+    event.respondWith(new Promise(function(resolve, reject) {
+        try {
+          var request = event.request;
+          if (url) {
+            request = new Request(url, init);
+          } else if (!params['noChange']) {
+            request = new Request(request, init);
+          }
+          fetch(request)
+            .then(function(res) {
+                // Send the result to fetch-access-control.html.
+                port.postMessage({fetchResult: 'resolved',
+                                  hasBody: !!res.body,
+                                  headers: headersToArray(res.headers),
+                                  type: res.type,
+                                  originalURL: originalURL});
+                resolve(res);
+              })
+            .catch(function(e) {
+                // Send the result to fetch-access-control.html.
+                port.postMessage({fetchResult: 'rejected'});
+                reject();
+              });
+        } catch (e) {
+          // Send the result to fetch-access-control.html.
+          port.postMessage({fetchResult: 'error'});
+          reject();
+        }
+      }));
+  });