Isolate Util Method To Be Near Usage

There was a stream utilty was that only be used in one class
(another utility class). The method was to get tracks, but it
sat along side other methods that look similar but were different
in very small ways.

This change moves that function to be in the same class as where
it is used so that it will be less distracting from the other
getTrack methods.

Change-Id: I21737b6b1341c06b41e6016e24b2b20ce5d40e77

lib/offline/stored_content_utils.js

@@ -53,7 +53,7 @@ shaka.offline.StoredContentUtils = class {
     let firstPeriod = manifest.periods[0];
 
     /** @type {!Array.<shaka.extern.Track>} */
-    let tracks = shaka.util.StreamUtils.getTracks(firstPeriod);
+    let tracks = shaka.offline.StoredContentUtils.getTracks_(firstPeriod);
 
     /** @type {shaka.extern.StoredContent} */
     let content = {
@@ -96,7 +96,7 @@ shaka.offline.StoredContentUtils = class {
     let metadata = manifestDB.appMetadata || {};
 
     /** @type {!Array.<shaka.extern.Track>} */
-    let tracks = shaka.util.StreamUtils.getTracks(firstPeriod);
+    let tracks = shaka.offline.StoredContentUtils.getTracks_(firstPeriod);
 
     /** @type {shaka.extern.StoredContent} */
     let content = {
@@ -111,4 +111,30 @@ shaka.offline.StoredContentUtils = class {
 
     return content;
   }
+
+
+  /**
+   * Gets track representations of all playable variants and all text streams.
+   *
+   * @param {shaka.extern.Period} period
+   * @return {!Array.<shaka.extern.Track>}
+   * @private
+   */
+  static getTracks_(period) {
+    const StreamUtils = shaka.util.StreamUtils;
+
+    const tracks = [];
+
+    const variants = StreamUtils.getPlayableVariants(period.variants);
+    for (const variant of variants) {
+      tracks.push(StreamUtils.variantToTrack(variant));
+    }
+
+    const textStreams = period.textStreams;
+    for (const stream of textStreams) {
+      tracks.push(StreamUtils.textStreamToTrack(stream));
+    }
+
+    return tracks;
+  }
 };

lib/util/stream_utils.js

@@ -350,32 +350,6 @@ shaka.util.StreamUtils.textStreamToTrack = function(stream) {
 };
 
 
-/**
- * Gets track representations of all playable variants and all text streams.
- *
- * @param {shaka.extern.Period} period
- * @return {!Array.<shaka.extern.Track>}
- */
-shaka.util.StreamUtils.getTracks = function(period) {
-  const StreamUtils = shaka.util.StreamUtils;
-
-  let tracks = [];
-
-  let variants = StreamUtils.getPlayableVariants(period.variants);
-  let textStreams = period.textStreams;
-
-  variants.forEach(function(variant) {
-    tracks.push(StreamUtils.variantToTrack(variant));
-  });
-
-  textStreams.forEach(function(stream) {
-    tracks.push(StreamUtils.textStreamToTrack(stream));
-  });
-
-  return tracks;
-};
-
-
 /**
  * Gets an array of Track objects for the given Period.
  *