Fix strange compiler problem in HLS parser.

Previously, the Closure compiler was causing a strange problem in
non-debug compiled builds in the HLS parser: when we make an alias for
shaka.net.NetworkingEngine.RequestType, if we access RequestType.SEGMENT
the value is undefined. However, if we store
shaka.net.NetworkingEngine.RequestType.SEGMENT in a variable, it works.
Looking at the compiled code, when shaka.net.NetworkingEngine.RequestType
is defined, SEGMENT seems to be treated as some special case, which might
explain this odd behavior.

Fixes #2156

Change-Id: I272dbc8b8db08ef8f9067c535c25890adae32440

lib/hls/hls_parser.js

@@ -1498,7 +1498,7 @@ shaka.hls.HlsParser = class {
    * @private
    */
   async fetchPartialSegment_(reference, fullOnly) {
-    const RequestType = shaka.net.NetworkingEngine.RequestType;
+    const requestType = shaka.net.NetworkingEngine.RequestType.SEGMENT;
 
     // Create two requests:
     //  1. A partial request meant to fetch the smallest part of the segment
@@ -1519,7 +1519,7 @@ shaka.hls.HlsParser = class {
         this.config_.retryParameters);
 
     if (fullOnly) {
-      return this.makeNetworkRequest_(fullRequest, RequestType.SEGMENT);
+      return this.makeNetworkRequest_(fullRequest, requestType);
     }
 
     // TODO(vaage): The need to do fall back requests is not likely to be unique
@@ -1531,7 +1531,7 @@ shaka.hls.HlsParser = class {
 
     try {
       const response = await this.makeNetworkRequest_(
-          partialRequest, RequestType.SEGMENT);
+          partialRequest, requestType);
 
       return response;
     } catch (e) {
@@ -1552,8 +1552,7 @@ shaka.hls.HlsParser = class {
                            'support Range requests and CORS preflights.',
       partialRequest.uris[0]);
 
-      const response = await this.makeNetworkRequest_(
-          fullRequest, RequestType.SEGMENT);
+      const response = await this.makeNetworkRequest_(fullRequest, requestType);
 
       return response;
     }
@@ -1939,7 +1938,7 @@ shaka.hls.HlsParser = class {
   async guessMimeType_(contentType, codecs, playlist) {
     const HlsParser = shaka.hls.HlsParser;
     const ContentType = shaka.util.ManifestParserUtils.ContentType;
-    const RequestType = shaka.net.NetworkingEngine.RequestType;
+    const requestType = shaka.net.NetworkingEngine.RequestType.SEGMENT;
 
     goog.asserts.assert(playlist.segments.length,
         'Playlist should have segments!');
@@ -1974,7 +1973,7 @@ shaka.hls.HlsParser = class {
     headRequest.method = 'HEAD';
 
     const response = await this.makeNetworkRequest_(
-        headRequest, RequestType.SEGMENT);
+        headRequest, requestType);
 
     const contentMimeType = response.headers['content-type'];
 
@@ -2035,12 +2034,12 @@ shaka.hls.HlsParser = class {
    * @private
    */
   requestManifest_(absoluteUri) {
-    const RequestType = shaka.net.NetworkingEngine.RequestType;
+    const requestType = shaka.net.NetworkingEngine.RequestType.MANIFEST;
 
     const request = shaka.net.NetworkingEngine.makeRequest(
         [absoluteUri], this.config_.retryParameters);
 
-    return this.makeNetworkRequest_(request, RequestType.MANIFEST);
+    return this.makeNetworkRequest_(request, requestType);
   }
 
   /**