Simplify frame loads in OriginReplication and SandboxFlagsReplication tests.

Recent work on didStopLoading makes it possible for us to use
WaitForLoadStop to wait for all child frames to be loaded when
navigating a subframe.

BUG=

Review URL: https://codereview.chromium.org/1123233005

Cr-Commit-Position: refs/heads/master@{#330155}
1 file changed