Remove Polymer 0.5.

third_party/polymer/components-chromium/core-focusable/polymer-mixin.js

-Polymer.mixin2 = function(prototype, mixin) {
-
-  // adds a single mixin to prototype
-
-  if (mixin.mixinPublish) {
-    prototype.publish = prototype.publish || {};
-    Polymer.mixin(prototype.publish, mixin.mixinPublish);
-  }
-
-  if (mixin.mixinDelegates) {
-    prototype.eventDelegates = prototype.eventDelegates || {};
-    for (var e in mixin.mixinDelegates) {
-      if (!prototype.eventDelegates[e]) {
-        prototype.eventDelegates[e] = mixin.mixinDelegates[e];
-      }
-    }
-  }
-
-  if (mixin.mixinObserve) {
-    prototype.observe = prototype.observe || {};
-    for (var o in mixin.mixinObserve) {
-      if (!prototype.observe[o] && !prototype[o + 'Changed']) {
-        prototype.observe[o] = mixin.mixinObserve[o];
-      }
-    }
-  }
-
-  Polymer.mixin(prototype, mixin);
-
-  delete prototype.mixinPublish;
-  delete prototype.mixinDelegates;
-  delete prototype.mixinObserve;
-
-  return prototype;
-};