Cherry pick Add LINKER_INITIALIZER marker to MemoryMappedFile::Region::kWholeFile

Cherry pick
https://src.chromium.org/viewvc/chrome?view=rev&revision=286423

Add LINKER_INITIALIZER marker to MemoryMappedFile::Region::kWholeFile

This is a follow-up to crrev.com/394313002. const initializers which
rely on the linker zero-initialization should use the LINKER_INITIALIZER
ctor for documentation purposes.
More discussion about this in the linked CL.

BUG=394502
Committed:
https://src.chromium.org/viewvc/chrome?view=rev&revision=286423

Bug: 16723226
Change-Id: I08c58204d0decaa013ca594e039d4966c00a1095
2 files changed