pub serve gets stuck, never serving files #2628
Description
Trying to get a component working, I found that having an html file that contains a non-empty <template> element caused pub serve to seemingly get stuck in an infinite loop (and never serve any requests).
@yjbanov suggested this had something to do with the dart Html5LibDomAdapter's appendChild shim returning null instead of throwing a not implemented exception. Changing this shim worked insofar as to make my component work, but now there is an exception logged:
Could not find Directive entry for formDirectives
<html template>
<html span>
<html template>
[Error from EmptyNgDepsRemover on examples|web/src/hello_world/index_dynamic.ng_deps.dart]:<html span>
Parsing ng templates failed.
Exception: not implemented
Stack Trace: #0 Html5LibDomAdapter.appendChild (package:angular2/src/dom/html_adapter.dart:132:5)
#1 ViewSplitter._addParentElement (package:angular2/src/render/dom/compiler/view_splitter.dart:103:9)
#2 ViewSplitter.process (package:angular2/src/render/dom/compiler/view_splitter.dart:88:14)
#3 CompileControl.internalProcess (package:angular2/src/render/dom/compiler/compile_control.dart:33:12)
#4 CompilePipeline._process (package:angular2/src/render/dom/compiler/compile_pipeline.dart:39:23)
#5 CompilePipeline._process (package:angular2/src/render/dom/compiler/compile_pipeline.dart:55:16)
#6 CompilePipeline.process (package:angular2/src/render/dom/compiler/compile_pipeline.dart:32:10)
#7 _TemplateExtractor.extractTemplates.<extractTemplates_async_body> (package:angular2/src/transform/template_compiler/generator.dart:107:18)
#8 _RootZone.runUnary (dart:async/zone.dart:1155)
#9 _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:494)
#10 _Future._propagateToListeners (dart:async/future_impl.dart:577)
#11 _Future._completeWithValue (dart:async/future_impl.dart:368)
#12 Future.wait.<anonymous closure> (dart:async/future.dart:299)
#13 _RootZone.runUnary (dart:async/zone.dart:1155)
#14 _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:494)
#15 _Future._propagateToListeners (dart:async/future_impl.dart:577)
#16 _Future._completeWithValue (dart:async/future_impl.dart:368)
#17 _Future._asyncComplete.<anonymous closure> (dart:async/future_impl.dart:422)
#18 _asyncRunCallbackLoop (dart:async/schedule_microtask.dart:41)
#19 _asyncRunCallback (dart:async/schedule_microtask.dart:48)
#20 _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:96)
#21 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:143)
This error is logged 3 times.