[iOS/GN] Convert //ios/third_party/earl_grey to build with GN.

ios/third_party/ochamcrest/BUILD.gn

 # 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")
 
-ios_framework_bundle("ochamcrest") {
+group("ochamcrest") {
+  testonly = true
+  public_deps = [
+    ":OCHamcrest.framework",
+  ]
+}
+
+ios_framework_bundle("OCHamcrest.framework") {
   testonly = true
   output_name = "OCHamcrest"
   sources = [
     "src/Source/Core/HCAssertThat.h",
     "src/Source/Core/HCAssertThat.m",
     "src/Source/Core/HCBaseDescription.h",
     "src/Source/Core/HCBaseDescription.m",
     "src/Source/Core/HCBaseMatcher.h",
     "src/Source/Core/HCBaseMatcher.m",
     "src/Source/Core/HCDescription.h",
@@ skipping 205 matching lines @@
   ]
 
   libs = [
     "Foundation.framework",
     "UIKit.framework",
   ]
 
   configs += [ "//build/config/compiler:enable_arc" ]
   configs -= [ "//build/config/gcc:symbol_visibility_hidden" ]
 }