Removed old media-internals page and rewrote it.

content/browser/resources/media/util/collapse.js

+/**
+ * @fileoverview Sets up the event handlers for the collapsing containers
+ */
+
+(function () {
+    "use strict";
+    var allCollapseDivs = document.querySelectorAll('.collapse');
+    goog.array.forEach(allCollapseDivs, function (elem) {
+        // find the header for the div, because we only want to trigger on that
+        var header = elem.querySelector("h2");
+        header.onclick = function () {
+            var wasOpen = elem.className.indexOf("open") !== -1;
+
+            if (wasOpen) {
+                elem.className = "collapse closed";
+            } else {
+                elem.className = "collapse open";
+            }
+        };
+    });
+
+}());