Add spec links for WebGL IDL files

third_party/WebKit/Source/modules/webgl/WebGLCompressedTextureS3TCsRGB.idl

 // 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.
 
+// https://www.khronos.org/registry/webgl/extensions/WEBGL_compressed_texture_s3tc_srgb/
+
 [
     DependentLifetime,
     NoInterfaceObject,
     DoNotCheckConstants,
 ] interface WebGLCompressedTextureS3TCsRGB {
     /* Compressed Texture Formats */
     const unsigned long COMPRESSED_SRGB_S3TC_DXT1_EXT        = 0x8C4C;
     const unsigned long COMPRESSED_SRGB_ALPHA_S3TC_DXT1_EXT  = 0x8C4D;
     const unsigned long COMPRESSED_SRGB_ALPHA_S3TC_DXT3_EXT  = 0x8C4E;
     const unsigned long COMPRESSED_SRGB_ALPHA_S3TC_DXT5_EXT  = 0x8C4F;
 };