metrics: Replace RankedList with RankedSet

Replace the O(n) access of std::list with O(log n) of std::set.

The overall overhead of RankedList is low, as it is only called periodically
from LeakDetectorImpl::TestForLeaks(). However, it has a high overhead
relative to TestForLeaks(). Using a set instead of a list will reduce overhead
during those moments with TestForLeaks() is called.

CPU overhead across entire renderer process, with sampling rate of 1/64:

                  TestForLeaks  RankedSet/List
                  ============  ==============
Using RankedList       0.0107%         0.0501%
Using RankedSet        0.0149%         0.0099%

The overhead of RankedList is 5x that of TestForLeaks(), while RankedSet has
an overhead less than that of TestForLeaks().

BUG=chromium:382705
TEST=components_unittests pass

Review URL: https://codereview.chromium.org/1826023002

Cr-Commit-Position: refs/heads/master@{#383067}

0 files changed, 0 insertions, 0 deletions