Adds mailto: URL support to app launching.

ios/chrome/browser/web/mailto_url_rewriter.h

Index: ios/chrome/browser/web/mailto_url_rewriter.h
diff --git a/ios/chrome/browser/web/mailto_url_rewriter.h b/ios/chrome/browser/web/mailto_url_rewriter.h
new file mode 100644
index 0000000000000000000000000000000000000000..186c7372d6ddad17dc69fa40522aec6a8aab9cc4
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+++ b/ios/chrome/browser/web/mailto_url_rewriter.h
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+// 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.
+
+#ifndef IOS_CHROME_BROWSER_WEB_MAILTO_URL_REWRITER_H_
+#define IOS_CHROME_BROWSER_WEB_MAILTO_URL_REWRITER_H_
+
+#import <Foundation/Foundation.h>
+
+@class MailtoHandler;
+class GURL;
+
+// Class of a singleton object that manages the available Mail client apps
+// and the selected Mail client app to handle mailto: URL scheme.
+@interface MailtoURLRewriter : NSObject
+
+// Returns the singleton instance.
++ (instancetype)sharedInstance;
+
+// Returns the ID as a string for the system-provided Mail client app.
++ (NSString*)systemMailApp;
+
+// Returns an array of all the currently supported Mail client apps that claims
+// to handle mailto: URL scheme through their own custom defined URL schemes.
+- (NSArray<MailtoHandler*>*)defaultHandlers;
+
+// Returns the ID as a string for the Mail client app was set to handle mailto:
+// URL scheme.
+- (NSString*)defaultHandlerID;
+
+// Sets the ID as a string for the Mail client app that will handle mailto:
+// URL scheme.
+- (void)setDefaultHandlerID:(NSString*)appStoreID;
+
+// Rewrites |gURL|, which must be a mailto: URL, into a new URL that can be
+// "opened" to launch the Mail client app.
+- (NSString*)rewriteMailtoURL:(const GURL&)gURL;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_WEB_MAILTO_URL_REWRITER_H_