Adds mailto: URL support to app launching.

ios/chrome/browser/web/mailto_handler.mm

Index: ios/chrome/browser/web/mailto_handler.mm
diff --git a/ios/chrome/browser/web/mailto_handler.mm b/ios/chrome/browser/web/mailto_handler.mm
new file mode 100644
index 0000000000000000000000000000000000000000..1f1d25b69082f6dfff76f3facb6fe2228dd59b7d
--- /dev/null
+++ b/ios/chrome/browser/web/mailto_handler.mm
@@ -0,0 +1,40 @@
+// 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.h"
+
+#import "base/strings/sys_string_conversions.h"
+#include "url/gurl.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@implementation MailtoHandler
+@synthesize appName = _appName;
+@synthesize appStoreID = _appStoreID;
+
+- (instancetype)initWithName:(NSString*)appName
+                  appStoreID:(NSString*)appStoreID {
+  self = [super init];
+  if (self) {
+    _appName = [appName copy];
+    _appStoreID = [appStoreID copy];
+  }
+  return self;
+}
+
+- (BOOL)isAvailable {
+  // This should be implemented by subclasses.
+  NOTREACHED();
+  return NO;
+}
+
+- (NSString*)rewriteMailtoURL:(const GURL&)gURL {
+  // This should be implemented by subclasses.
+  NOTREACHED();
+  return nil;
+}
+
+@end