Convert ios_web_shell_test to GN.

ios/third_party/earl_grey/ios_eg_test.gni

+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//build/config/ios/rules.gni")
+
+# EarlGrey tests are just XCTests that also depends on EarlGrey.
+template("ios_eg_test") {
+  ios_xctest_test(target_name) {
+    forward_variables_from(invoker, "*")
+    if (!defined(bundle_deps)) {
+      bundle_deps = []
+    }
+    bundle_deps += [
+      "//ios/third_party/earl_grey:earl_grey+bundle",
+      "//ios/third_party/ochamcrest:ochamcrest+bundle",
+    ]
+    if (!defined(deps)) {
+      deps = []
+    }
+    deps += [
+      "//ios/third_party/earl_grey:earl_grey+link",
+      "//ios/third_party/ochamcrest:ochamcrest+link",
+    ]
+  }
+}
+
+set_defaults("ios_eg_test") {
+  configs = default_executable_configs
+}