Cancel the JumpList update if top 5 most visited URLs are unchanged

Previously, if TopSites service detects any changes in the top 24 most
visited URLs, a JumpList update is scheduled. However, since only the
top 5 URLs are displayed in JumpList, updates caused by the changes
outside of the top 5 URLs are wasted. This CL trims out that waste.

BUG=40407, 179576, 715902, 717236, 498987

Review-Url: https://codereview.chromium.org/2896233003
Cr-Commit-Position: refs/heads/master@{#476017}
7 files changed