fix(Tizen): Fix src= playback on Tizen 3

src= playback on Tizen 3 was stalled at time 0, causing automated test
failures.  These went unnoticed while our Tizen device in the lab was
offline.

The only workaround I was able to find was to call load(), which we
recently stopped doing for src= playback.  This adds it back, but only
for Tizen.

Found while investigating #2620.

Backported to v2.5.x

Change-Id: I4e071a6f1ccb18b9891dfc646a22dbb8c1711eb4

lib/player.js

@@ -1996,6 +1996,14 @@ shaka.Player.prototype.onSrcEquals_ = function(has, wants) {
   // current time because |playhead| will do that for us.
   has.mediaElement.src = has.uri;
 
+  // Tizen 3 won't load anything unless you call load() explicitly, no matter
+  // the value of the preload attribute.  This is harmful on some other
+  // platforms by triggering unbounded loading of media data, but is necessary
+  // here.
+  if (shaka.util.Platform.isTizen()) {
+    has.mediaElement.load();
+  }
+
   // Set the load mode last so that we know that all our components are
   // initialized.
   this.loadMode_ = shaka.Player.LoadMode.SRC_EQUALS;