RDH:  Ensure there's at most one LoadInfoList in flight.

ResourceDispatcherHost pushes pending load state of all frames to the UI
thread once every 250 milliseconds when there's a pending load.  This
happens even when the UI thread is blocked.  Apparently it's causing an
OOM when the UI thread is blocked.  Whatever is blocking the UI thread
is another issue entirely, but we shouldn't use unbounded memory in the
browser process.  This CL prevents load state updates from being sent
until the previous set was ACKed by the UI thread.

Bug: 824869
TBR: [email protected]
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: I3b68522c5281d477d3a621ac02e5df1f75153d99
Reviewed-on: https://chromium-review.googlesource.com/978383
Commit-Queue: Matt Menke <[email protected]>
Reviewed-by: John Abd-El-Malek <[email protected]>
Reviewed-by: Charlie Harrison <[email protected]>
Cr-Commit-Position: refs/heads/master@{#545616}
3 files changed