Add support for loading API keys from Info.plist on iOS and macOS.

google_apis/google_api_keys_mac.mm

+// 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 "google_api_keys_mac.h"
+
+#include "base/mac/bundle_locations.h"
+#include "base/mac/foundation_util.h"
+#include "base/strings/sys_string_conversions.h"
+
+namespace google_apis {
+
+std::string GetAPIKeyFromInfoPlist(const std::string& key_name) {
+  NSString* keyName = base::SysUTF8ToNSString(key_name);
+  NSString* keyValue = base::mac::ObjCCast<NSString>(
+      [base::mac::FrameworkBundle() objectForInfoDictionaryKey:keyName]);
+  return base::SysNSStringToUTF8(keyValue);
+}
+
+}  // namespace google_apis