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Chrome's main thread needs a 1.5 MiB stack size in order to avoid stack
overflow crashes. However if this is set in the PE file then other
threads get this size as well, leading to address-space exhaustion in
32-bit Chrome. For threads that we create we can set the size explicitly
but for some OS threads (the spell checker and those in the Windows
thread pool) they end up with the 1.5 MiB default set in the PE file.

This change tries to control this by setting the default thread size
(in the PE file) to 1.0 MiB and then creating and switching to a fiber
with a 1.5 MiB stack.

This dance wastes 1.0 MiB of address space (for the initial stack that
is never used) but then saves 0.5 MiB of address space for every thread
that doesn't specify a stack size. At startup time on my laptop there
are 13 threads (plus the main thread) with 1.5 MiB stacks, so this
change saves 13*0.5 MiB - 1.0 MiB = 5.5 MiB of address space.

It is quite likely that the default stack size can be dropped to 0.5
MiB which would save another 7 MiB of address space at startup.

Bug: 981238, 1023804
Change-Id: Iabc9d86758a8a9fb77761a5a43a9b11278f4effa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2425743
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813553}