[ServiceWorker] Provide more descriptive error messages when fetch API fails.

LayoutTests/http/tests/serviceworker/chromium/resources/fetch-error-messages-worker.js

+importScripts('../../resources/worker-testharness.js');
+importScripts('../../resources/test-helpers.js');
+
+async_test(function(t) {
+    var url = get_host_info()['HTTP_REMOTE_ORIGIN'] + '/dummy.html';
+    fetch(new Request(url, {mode: 'same-origin'}))
+      .then(
+        t.unreached_func('Fetching must fail.'),
+        function(e) {
+          assert_equals(
+            e.message,
+            'Fetch API cannot load ' + url + '. ' +
+            'Request mode is "same-origin" but the URL\'s origin is not same ' +
+            'as the request origin ' + get_host_info()['HTTP_ORIGIN']  + '.');
+          t.done();
+        })
+      .catch(unreached_rejection(t));
+  }, 'Fetch API error message - not same origin request');
+
+async_test(function(t) {
+    var url = 'ftp://example.com/dummy.html';
+    fetch(new Request(url, {mode: 'cors'}))
+      .then(
+        t.unreached_func('Fetching must fail.'),
+        function(e) {
+          assert_equals(
+            e.message,
+            'Fetch API cannot load ' + url + '. ' +
+            'URL scheme must be "http" or "https" for CORS request.');
+          t.done();
+        })
+      .catch(unreached_rejection(t));
+  }, 'Fetch API error message - non http cors request');
+
+async_test(function(t) {
+    var url = 'about://blank';
+    fetch(new Request(url))
+      .then(
+        t.unreached_func('Fetching must fail.'),
+        function(e) {
+          assert_equals(
+            e.message,
+            'Fetch API cannot load ' + url + '. ' +
+            'URL scheme "about" is not supported.');
+          t.done();
+        })
+      .catch(unreached_rejection(t));
+  }, 'Fetch API error message - unsupported scheme.');
+
+async_test(function(t) {
+    var url =
+        new URL(get_host_info()['HTTP_ORIGIN'] + base_path() +
+                '../../resources/invalid-chunked-encoding.php').toString();
+    fetch(new Request(url))
+      .then(
+        t.unreached_func('Fetching must fail.'),
+        function(e) {
+          assert_equals(
+            e.message,
+            'Fetch API cannot load ' + url + '. ' +
+            'net::ERR_INVALID_CHUNKED_ENCODING');
+          t.done();
+        })
+      .catch(unreached_rejection(t));
+  }, 'Fetch API error message - invalid chunked encoding.');
+
+async_test(function(t) {
+    var url =
+        new URL(get_host_info()['HTTP_REMOTE_ORIGIN'] + base_path() +
+                '../../resources/fetch-access-control.php').toString();
+    fetch(new Request(url))
+      .then(
+        t.unreached_func('Fetching must fail.'),
+        function(e) {
+          assert_equals(
+            e.message,
+            'Fetch API cannot load ' + url + '. ' +
+            'No \'Access-Control-Allow-Origin\' header is present on the ' +
+            'requested resource. Origin \'' + get_host_info()['HTTP_ORIGIN'] +
+            '\' is therefore not allowed access.');
+          t.done();
+        })
+      .catch(unreached_rejection(t));
+  }, 'Fetch API error message - cors error.');
+
+async_test(function(t) {
+    // FIXME: When we support the redirection in Fech API, we have to change
+    // this test case.
+    var redirect = 'http://www.example.com';
+    var url =
+        new URL(get_host_info()['HTTP_REMOTE_ORIGIN'] + base_path() +
+                '../../resources/redirect.php?Redirect=' + redirect).toString();
+    fetch(new Request(url))
+      .then(
+        t.unreached_func('Fetching must fail.'),
+        function(e) {
+          assert_equals(
+            e.message,
+            'Fetch API cannot load ' + url + '. ' +
+            'Redirects are not yet supported.');
+          t.done();
+        })
+      .catch(unreached_rejection(t));
+  }, 'Fetch API error message - redirect error.');