Record swap metrics
This CL adds SwapMetricsObserver which records swap rates and reports
them as platform-specific metrics. The purpose of adding these metrics
is to measure the impact of actions we take to free up memory. If we
aggressively free up memory under high memory pressure, we may touch
pages which are already swapped out (or compressed). In such cases
thrashing could happen and we are making the situation worse.
Swap rates and page compression/decompression rate would be good
indicators of thrashing. Metrics will be recorded every 60 seconds.
This CL only adds metrics for Android/ChromeOS/Linux. Follow-up CLs
will add them for macOS.
BUG=617492
Review-Url: https://codereview.chromium.org/2824133002
Cr-Commit-Position: refs/heads/master@{#468266}
9 files changed
