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VC++ PGO builds crash deep inside memmove, as called by
message_center::InnerBoundedLabel::GetSizeForWidthAndLines which calls
base::JoinString and then ultimately basic_string<>::append and memmove.
Inspection of the stack and the generated code shows that
base::JoinString is called correctly but that base::JoinString (or the
inlined JoinStringT and three other levels of inlining) fail to read
separator off the stack correctly - they read it from an address that is
four bytes too early. This leads to copying too many bytes from the
wrong address.

Fully disabling optimizations in VC++ builds for the affected function
seems like the right fix. If time permits then a reduction and VC++ bug
will be created. However if this is a PGO-only bug then...

Bug: 804884
Change-Id: I80fd8e693a35b26a386cd99a1b17c54bede95d5c
Reviewed-on: https://chromium-review.googlesource.com/891569Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532658}