Make sure that ExpressRoute only matches same-origin requests

[jeffposnick]

Right now the goog.routing.ExpessRoute just looks at .pathname of the request URL, and compares it to the path used to the configure the route.

This means that a request for https://cross-domain.com/path/to/file would match a route that was configured with new ExpressRoute({path: '/path/to/file', hander}), even if the service worker were served from https://example.com.

I think the decision was made not to support that additional origin configuration option that sw-toolbox supported, and which was pretty confusing. (@gauntface @addyosmani, can you confirm that's what we decided?)

I'll point out in the docs that ExpressRoute should only be used for same-origin routing, and if cross-origin routes are needed, something like RegExpRoute is a better choice.

[gauntface]

This sounds good to me.

I was never a fan of the origin parameter in sw-toolbox and I feel that developers should be more cautious with third party requests so LGTM.