Fix InitializeSpecShim is not defined issue

[huningxin]

Fix #63

[huningxin]

@toji , PTAL. Thanks!

[toji]

Hm, upon looking at this it seems that the function name was a typo? We probably want the pages to be calling "InstallWebVRSpecShim" instead, to avoid ambiguity and having two names for the same thing. As for the function not being exported, that should be fixed in the main polyfill library so that we don't lose this change the next time we update from source.

[huningxin]

From the log, it seems the InstallWebVRSpecShim patch is lost in latest webvr-polyfill update commit.

Fix in the webvr-polyfill library sounds a better solution. I will do that.

[huningxin]

I send a PR immersive-web/webvr-polyfill#259 to expose InstallWebVRSpecShim. Once webvr-polyfill is updated, all samples need to replace InitializeSpecShim with InstallWebVRSpecShim.

[huningxin]

Updated the PR, @toji , please take another look. Thanks!

[huningxin]

ping @toji . Thanks!

[toji]

Thanks for your work on this and sorry it was never merged. The issue has been rendered moot by #85