clovis: Add the timing heuristic to request_dependency_graph.

This heuristic is taken from loading_model, and is a required step to
complete the refactoring of loading_model. It also provides better
results for prefetch_view, which uses dependency_graph.

Review URL: https://codereview.chromium.org/1848443002

Cr-Commit-Position: refs/heads/master@{#383968}
4 files changed