Wait for all bootstrap paths to be cached

Repeating this needs an empty cache and a physical android device. It's a race condition but it's clear from the code what needs to change.

waitForCache is not waiting for all the files which bootstrap needs before calling it.

The resulting error is "cannot read source of undefined". Screenshot attached to see the debugging which confirms what is described.

My suggested patch is

function waitForCore(cb) {
    // we only care if goog/base.js is actually in the cache, that's enough
    // to bootstrap regardless whether some things must be refetched
    if(KRELL_CACHE.ready
       && KRELL_CACHE.has(toPath("goog/base.js"))
       && KRELL_CACHE.has(toPath("goog/deps.js"))
       && KRELL_CACHE.has(toPath("cljs_deps.js"))
       && KRELL_CACHE.has(toPath("krell_repl_deps.js"))) {
        bootstrap();
        cb();
    } else if(typeof cljs !== 'undefined') {
        cb();
    } else {
        setTimeout(function() { waitForCore(cb); }, 250);
    }
}

Steps to repeat are fiddly but could probably be refined

start a fresh repl
uninstall and reinstall the app on the android device
The adb logcat will show KRELL Bootstrap from cache failed if the race condition happened
throw the error after that log statement

I was able to see the error more easily after using the chrome debug tools to pause on the exception. To do that I needed to delay the cache initialisation by triggering tryConnection manually. It was all a bit messy but I suspect you know good ways to break on that exception and see the behaviour.

vouch-opensource / krell

Wait for all bootstrap paths to be cached #98