Consider shared libs when precreating WebView classloader.

The change to handling of the deprecated Apache HTTP library means that
the WebView implementation package might have a non-empty shared library
list. Make sure to fetch shared libraries when querying WebView
implementations, and take them into account when constructing both the
actual classpath to be used to precreate the classloader, and when
deciding what the cache key for the precreated classloader should be.

Change-Id: I5e1409358d935e1c9f325db434bc6d4ef8ead759
Fixes: 65574359
Test: launch anything that uses WebView