Bundled entrypoints are actually emitted *twice* (once in original form, once in bundled form)

[usergenic]

The BuildBundler transform stream sends everything through and then after it bundles, it sends the bundle files through, typically with the same name as the fragment.

Example:

project.sources().*      project.bundler().*
- fragment1.html         - fragment1.html
- fragment2.html     =>  - fragment2.html
- script.js              - script.js
                         - fragment1.html
                         - fragment2.html

In practice, this is not causing problems for people, because the subsequent bundled files wind up overwriting the previous ones in a typical gulp stream setup. But when this winds up causing problems it may be very confusing to our users to diagnose and correct.

For this reason, we need to stop the output of bundled filenames. The downside is that the naive fix will be to hold up all html files in the stream until after bundling, which creates a bottleneck, but fixing this will dovetail with a fix for https://github.com/Polymer/polymer-build/issues/70 anyways.

[usergenic]

cc @FredKSchott

[usergenic]

Working on a solution for this, but will depend on Polymer/polymer-bundler#464