Port 99023682

Original commit message:

    The scheduler expects a trimmed graph, so we have to trim the graph
    before scheduling.

R=ahaas@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com

BUG=
LOG=N

Review-Url: https://chromiumcodereview.appspot.com/2431093004
Cr-Commit-Position: refs/heads/master@{#40475}