[Android] Fix a subtle issue in Java Bridge regarding interfaces removal

Update JavaBridgeBasicsTest.testRemovalNotReflectedUntilReload to actually
call Java GC after removing the interface, and verify that the Java object
is still callable from the page side. Fix the code to make the test pass.

BUG=437761

Review URL: https://codereview.chromium.org/767453003

Cr-Commit-Position: refs/heads/master@{#306176}
2 files changed