Adds mailto: URL support to app launching.

ios/chrome/browser/web/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("//ios/web/js_compile.gni")
 
 source_set("web") {
   configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "dom_altering_lock.h",
@@ skipping 166 matching lines @@
     "blocked_popup_tab_helper.h",
     "blocked_popup_tab_helper.mm",
     "chrome_web_client.h",
     "chrome_web_client.mm",
     "error_page_content.h",
     "error_page_content.mm",
     "error_page_generator.h",
     "error_page_generator.mm",
     "external_app_launcher.h",
     "external_app_launcher.mm",
+    "mailto_handler.h",
+    "mailto_handler.mm",
+    "mailto_handler_gmail.h",
+    "mailto_handler_gmail.mm",
+    "mailto_handler_system_mail.h",
+    "mailto_handler_system_mail.mm",
+    "mailto_url_rewriter.h",
+    "mailto_url_rewriter.mm",
     "passkit_dialog_provider.h",
     "print_observer.h",
     "print_observer.mm",
   ]
   deps = [
     ":chrome_bundle",
     ":resources",
     "//base",
     "//components/content_settings/core/browser",
     "//components/dom_distiller/core",
@@ skipping 46 matching lines @@
 
 source_set("unit_tests_internal") {
   configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "auto_reload_controller_unittest.mm",
     "blocked_popup_tab_helper_unittest.mm",
     "chrome_web_client_unittest.mm",
     "error_page_generator_unittest.mm",
     "external_app_launcher_unittest.mm",
+    "mailto_handler_gmail_unittest.mm",
+    "mailto_handler_system_mail_unittest.mm",
+    "mailto_handler_unittest.mm",
+    "mailto_url_rewriter_unittest.mm",
   ]
   deps = [
     ":test_support",
     ":web_internal",
     "//base",
     "//base/test:test_support",
     "//components/content_settings/core/browser",
     "//components/infobars/core",
     "//ios/chrome/browser/browser_state:test_support",
     "//ios/chrome/browser/content_settings:content_settings",
@@ skipping 63 matching lines @@
     "early_page_script_perftest.mm",
   ]
   deps = [
     "//base",
     "//ios/chrome/test/base:perf_test_support",
     "//ios/web",
     "//ios/web:test_support",
   ]
   libs = [ "WebKit.framework" ]
 }