Bring back SchemeRegistry::RegisterURLSchemeAsCORSEnabled()

Removed in https://crrev.com/c/530888 and https://crrev.com/c/584663.

It is used by Electron to implement API method
`webFrame.registerURLSchemeAsPrivileged()` [1].
`corsEnabled` option of this method defaults to `true` and removing it
without having an alternative way to mark a certain URL scheme
as CORS enabled would break some application that use Electron.

It would be great if Chromium could keep `RegisterURLSchemeAsCORSEnabled()`
method to make Electron's maintainers and users life a little bit easier.

[1] https://electron.atom.io/docs/api/web-frame/#webframeregisterurlschemeasprivilegedscheme-options

R=mkwst@chromium.org, tyoshino@chromium.org

Bug: 
Change-Id: Ifc548df6472db45111e8c32fe9efea4a50baa2a0
Reviewed-on: https://chromium-review.googlesource.com/768808
Commit-Queue: Takeshi Yoshino <tyoshino@chromium.org>
Reviewed-by: Takeshi Yoshino <tyoshino@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519055}

AUTHORS

@@ -41,6 +41,7 @@ Alexandre Abreu <wiss1976@gmail.com>
 Alexandru Chiculita <achicu@adobe.com>
 Alexey Korepanov <alexkorep@gmail.com>
 Alexey Kuts <kruntuid@gmail.com>
+Alexey Kuzmin <alex.s.kuzmin@gmail.com>
 Alexis Brenon <brenon.alexis@gmail.com>
 Alexis La Goutte <alexis.lagoutte@gmail.com>
 Alexis Menard <alexis.menard@intel.com>

third_party/WebKit/Source/platform/weborigin/SchemeRegistry.cpp

@@ -217,6 +217,11 @@ bool SchemeRegistry::ShouldTreatURLSchemeAsNotAllowingJavascriptURLs(
       scheme);
 }
 
+void SchemeRegistry::RegisterURLSchemeAsCORSEnabled(const String& scheme) {
+  DCHECK_EQ(scheme, scheme.DeprecatedLower());
+  GetMutableURLSchemesRegistry().cors_enabled_schemes.insert(scheme);
+}
+
 bool SchemeRegistry::ShouldTreatURLSchemeAsCORSEnabled(const String& scheme) {
   DCHECK_EQ(scheme, scheme.DeprecatedLower());
   if (scheme.IsEmpty())

third_party/WebKit/Source/platform/weborigin/SchemeRegistry.h

@@ -87,6 +87,11 @@ class PLATFORM_EXPORT SchemeRegistry {
       const String& scheme);
 
   // Allow non-HTTP schemes to be registered to allow CORS requests.
+  // This is not used in Chromium anymore but left here intentionally
+  // to allow other embedders of Blink to add more schemes
+  // to the CORS-enabled schemes list.
+  // As for now (Nov 2017) it is used by Electron.
+  static void RegisterURLSchemeAsCORSEnabled(const String& scheme);
   static bool ShouldTreatURLSchemeAsCORSEnabled(const String& scheme);
 
   // Serialize the registered schemes in a comma-separated list.