Adds mailto: URL support to app launching.

ios/chrome/browser/web/mailto_handler_gmail.mm

Index: ios/chrome/browser/web/mailto_handler_gmail.mm
diff --git a/ios/chrome/browser/web/mailto_handler_gmail.mm b/ios/chrome/browser/web/mailto_handler_gmail.mm
new file mode 100644
index 0000000000000000000000000000000000000000..39ba91a5b354fe7c44c5d9bf0ee744096b297fb2
--- /dev/null
+++ b/ios/chrome/browser/web/mailto_handler_gmail.mm
@@ -0,0 +1,35 @@
+// Copyright 2017 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 "ios/chrome/browser/web/mailto_handler_gmail.h"
+#include "base/strings/sys_string_conversions.h"
+#include "url/gurl.h"
+#include "url/url_constants.h"
+
+#import <UIKit/UIKit.h>
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@implementation MailtoHandlerGmail
+
+- (instancetype)init {
+  // Gmail product name is not supposed to be localized.
+  self = [super initWithName:@"Gmail" appStoreID:@"422689480"];
+  return self;
+}
+
+- (BOOL)isAvailable {
+  // Checks if Gmail app is installed on this device. This assumes that
+  // "googlegmail" has been whitelisted in Chrome's Info.plist.
+  return [[UIApplication sharedApplication]
+      canOpenURL:[NSURL URLWithString:@"googlegmail://"]];
+}
+
+- (NSString*)beginningScheme {
+  return @"googlegmail:/co?";
+}
+
+@end