UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.86 Safari/537.36

Steps to reproduce the problem:
1. Connect the Shield controller via USB to a Mac
2. Go to http://html5gamepad.com/
3. Test buttons, sticks, and triggers

What is the expected behavior?
Most buttons and axes should at least appear in the gamepad output somewhere. The Windows mapping for the Shield controller has all buttons working except the select button. Mac should match this level of functionality.

What went wrong?
None of the sticks, triggers, or d-pad buttons work at all. Only the L2, L3, R2, R3, and the X button work.

Did this work before? No 

Chrome version: 52.0.2718.0  Channel: canary
OS Version: OS X 10.11.4
Flash Version: Shockwave Flash 21.0 r0

This issue is caused by the fact that IOHIDDeviceCopyMatchingElements() in gamepad_platform_data_fetcher_mac.mm doesn't exclude HID elements that aren't within our desired application containers. The Shield controller contains several top-level HID application containers. Because the code in the data fetcher parses elements without regard for their container's usage, this causes the available space in the WebGamepad object to be rapidly exhausted. Once we finally get to the HID elements we want, the indices for buttons and axes are already filled.