Use newly fetched PackageInfo for loading WebView code.

During a time window between the point at which a webview package
becomes updated and the WebViewUpdateService receiving an intent
declaring this action the WebViewUpdateService APIs will return a
PackageInfo pointing to an old and possibly removed WebView package.
This means that any paths that PackageInfo is referring to could have
been removed.

Currently, we set WebViewFactory.sPackageInfo using one of these APIs
and we might thus try to use deleted paths to to load WebView. This can
cause crashes, so instead fetch a fresh PackageInfo and assign
WebViewFactory.sPackageInfo to that.

Also early-out in loadWebViewNativeLibraryFromPackage if the current
package version doesn't match that of the one fetched from the
WebViewUpdateService.

Bug: 29381682
Change-Id: I2713ce2338a4a96c5317dcdbb363b424513088d5