watch the registration queue and print if it has no progress

pkg/polymer/CHANGELOG.md

 #### 0.15.0-dev
   * Added Polymer.forceReady method. This forces a ready state regardless of
     whether or not there are still polymer-element declarations waiting for
     their class definitions to be loaded.
   * Added Polymer.waitingFor method. This returns a list of all polymer-element
     declarations that are still waiting for their class definitions to be
     loaded.
+  * Add runtime checking of the waitingFor queue and print to the console if a
+    deadlock situation is suspected to help diagnose the white screen of death.
   * Added injectBoundHTML instance method. This can be used to dynamically
     inject html that is bound to your current element into a target element.
 
 #### 0.14.3
   * Warn if the same css file is inlined more than once,
     [19996](http://dartbug.com/19996).
   * Don't start moving elements from head to body until we find the first
     import, [20826](http://dartbug.com/20826).
   * Add option to not inject platform.js in the build output
     [20865](http://dartbug.com/20865). To use, set `inject_platform_js` to
@@ skipping 245 matching lines @@
 #### 0.9.2+3
   * fix [15574](https://code.google.com/p/dart/issues/detail?id=15574),
     event bindings in dart2js, by working around issue
     [15573](https://code.google.com/p/dart/issues/detail?id=15573)
 
 #### 0.9.2+2
   * fix enteredView in dart2js, by using custom_element >= 0.9.1+1
 
 [6ad2d61]:https://github.com/Polymer/polymer-dev/commit/6a3e1b0e2a0bbe546f6896b3f4f064950d7aee8f
 [3b690ad]:https://github.com/Polymer/polymer-dev/commit/3b690ad0d995a7ea339ed601075de2f84d92bafd