DevTools: Profiler domain refactoring: encode timestamps as deltas.

The CL makes CPUProfile encode sample timestamps as deltas, which makes the
representation more compact.
startTime and endTime are represented in microseconds rather than seconds.

BUG=635947

Review-Url: https://codereview.chromium.org/2262543002
Cr-Original-Commit-Position: refs/heads/master@{#413332}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 68666c0876081db75338384d7b76f0b5fb84473e
2 files changed