[polymer] custom event handler matching is case sensitive

[DartBot]

This issue was originally filed by Erik.G...@gmail.com

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What steps will reproduce the problem?

1. Create a custom element
2. Attach a custom event handler to the element 'on-polymerSelect'.
3. Call this.fire('polymerSelect').

What is the expected output? What do you see instead?

The handler bound to on-polymerSelect should fire.

The handler doesn't fire.

What version of the product are you using? On what operating system?

0.8.9 build 19720

Please provide any additional information below.

If the name of the handler is case insensitive, then firing the event should be case insensitive as well. Otherwise, event names have to be all lowercase which make them difficult to read and write. You
can improve legibility with underscores, but then you get funky event handlers line on-polymer_select.

[dgrove]

Added Area-Polymer, Triaged labels.

[jmesserly]

fyi, polymer uses dash ("-") in their examples. That would be my recommendation.

[jmesserly]

Polymer/polymer#340

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Added MovedToGithub label.