Since code objects cannot grow larger than 2GB anyway, it's enough to
store the instruction offset and landing pad offset as 32-bit values.
This reduces the size of the ProtectedInstructionData struct by 50%.

R=eholk@chromium.org

Bug: v8:5277
Change-Id: I4d2e0dc76b8a853fb50d51d70d5ec4038ee594ac
Reviewed-on: https://chromium-review.googlesource.com/686757
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Eric Holk <eholk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48192}