When simulating an H2 download with h2OverflowBytesDownloaded > 0,
TCPConnection.simulateDownloadUntil subtracts h2OverflowBytesDownloaded
from bytesToDownload and returns only the newly downloaded bytes in
calculation.bytesDownloaded.

When another node (such as a parallel CPUNode) finished mid-download:

1. Simulator.updateProgressMadeInTimePeriod updated
   connection.h2OverflowBytesDownloaded to
   calculation.extraBytesDownloaded without adding the consumed
   overflow bytes to timingData.bytesDownloaded, causing those bytes
   to be downloaded a second time on subsequent steps.
2. On an unwarmed H2 connection, TCPConnection.simulateDownloadUntil
   only applied h2OverflowBytesDownloaded when this.warmed was true, so
   overflow bytes produced during an intermediate step of the initial
   request were wiped out on the final step before setWarmed(true).

Bug: 570004155
Change-Id: I13434e8bcab14f7eace06d3ef14b0848f88fea80
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/8511806
Reviewed-by: Paul Irish <paulirish@chromium.org>
Commit-Queue: Connor Clark <cjamcl@chromium.org>