Adds mailto: URL support to app launching.

ios/chrome/browser/web/BUILD.gn

Index: ios/chrome/browser/web/BUILD.gn
diff --git a/ios/chrome/browser/web/BUILD.gn b/ios/chrome/browser/web/BUILD.gn
index ef89fc6290b0054bbb19e8957d19bf06a411c734..cf0ffd39d09fb5c38701a97b9f09ba8f05a332da 100644
--- a/ios/chrome/browser/web/BUILD.gn
+++ b/ios/chrome/browser/web/BUILD.gn
@@ -184,6 +184,14 @@ source_set("web_internal") {
     "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",
@@ -250,6 +258,10 @@ source_set("unit_tests_internal") {
     "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",