fix: Fix choosing tracks from streaming event (shaka-project#3459)

In v2.5, we could choose a track explicitly from the "streaming" event.  In v3, this was broken.  Now the player will not choose any tracks automatically if explicit tracks were chosen by the app during the "streaming" event.

Closes shaka-project#3448

lib/player.js

@@ -1866,34 +1866,56 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
     this.dispatchEvent(this.makeEvent_(shaka.Player.EventName.Streaming));
 
     // Pick the initial streams to play.
-    const initialVariant = this.chooseVariant_();
-    goog.asserts.assert(initialVariant, 'Must choose an initial variant!');
-    this.switchVariant_(initialVariant, /* fromAdaptation= */ true,
-        /* clearBuffer= */ false, /* safeMargin= */ 0);
+    // however, we would skip switch to initial variant
+    // if user already pick variant track (via selectVariantTrack api)
+    let initialVariant = null;
+    const activeVariantTrack = this.getVariantTracks().find((t) => t.active);
+
+    if (!activeVariantTrack) {
+      initialVariant = this.chooseVariant_();
+      goog.asserts.assert(initialVariant, 'Must choose an initial variant!');
+      this.switchVariant_(initialVariant, /* fromAdaptation= */ true,
+          /* clearBuffer= */ false, /* safeMargin= */ 0);
+
+      // Now that we have initial streams, we may adjust the start time to align
+      // to a segment boundary.
+      if (this.config_.streaming.startAtSegmentBoundary) {
+        const startTime = this.playhead_.getTime();
+        const adjustedTime =
+            await this.adjustStartTime_(initialVariant, startTime);
+
+        this.playhead_.setStartTime(adjustedTime);
+      }
 
-    // Decide if text should be shown automatically.
-    const initialTextStream = this.chooseTextStream_();
-    if (initialTextStream) {
-      this.addTextStreamToSwitchHistory_(
-          initialTextStream, /* fromAdaptation= */ true);
+      // Since the first streams just became active, send an adaptation event.
+      this.onAdaptation_(null,
+          shaka.util.StreamUtils.variantToTrack(initialVariant));
     }
 
-    this.setInitialTextState_(initialVariant, initialTextStream);
-    // Don't initialize with a text stream unless we should be streaming text.
-    if (initialTextStream && this.shouldStreamText_()) {
-      this.streamingEngine_.switchTextStream(initialTextStream);
-    }
+    // Decide if text should be shown automatically.
+    // similar to video/audio track, we would skip switch initial text track
+    // if user already pick text track (via selectTextTrack api)
+    const activeTextTrack = this.getTextTracks().find((t) => t.active);
 
-    // Now that we have initial streams, we may adjust the start time to align
-    // to a segment boundary.
-    if (this.config_.streaming.startAtSegmentBoundary) {
-      const startTime = this.playhead_.getTime();
-      const adjustedTime =
-          await this.adjustStartTime_(initialVariant, startTime);
+    if (!activeTextTrack) {
+      const initialTextStream = this.chooseTextStream_();
 
-      this.playhead_.setStartTime(adjustedTime);
+      if (initialTextStream) {
+        this.addTextStreamToSwitchHistory_(
+            initialTextStream, /* fromAdaptation= */ true);
+      }
+
+      if (initialVariant) {
+        this.setInitialTextState_(initialVariant, initialTextStream);
+      }
+
+      // Don't initialize with a text stream unless we should be streaming text.
+      if (initialTextStream && this.shouldStreamText_()) {
+        this.streamingEngine_.switchTextStream(initialTextStream);
+      }
     }
 
+
     // Start streaming content. This will start the flow of content down to
     // media source.
     await this.streamingEngine_.start();
@@ -1908,10 +1930,6 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
     // Dispatch a 'trackschanged' event now that all initial filtering is done.
     this.onTracksChanged_();
 
-    // Since the first streams just became active, send an adaptation event.
-    this.onAdaptation_(null,
-        shaka.util.StreamUtils.variantToTrack(initialVariant));
-
     // Now that we've filtered out variants that aren't compatible with the
     // active one, update abr manager with filtered variants.
     // NOTE: This may be unnecessary.  We've already chosen one codec in