Merge jumplist delete task and update task

This allows consistent comparison of time cost to the previous versions
of jumplist implementation.

Code-wise, it merges the DeleteDirectoryAndLogResults method into the
RunUpdateJumplist method.

This CL also logs the execution time of DeleteDirectoryContentAndLogResults
to UMA.

BUG=40407, 179576

Review-Url: https://codereview.chromium.org/2827563002
Cr-Commit-Position: refs/heads/master@{#465136}
3 files changed