This fixes the collection of function sizes (see comment #1 of
v8:6361).  This was done by adding a wrapper function around
VerifyWasmCode() that updates UMA stats for function size (as well as
decode time when validating).

Bug: v8:6361
Change-Id: Ia2597db22cbed5b0429d9c8514e96cdea5d7323a
Reviewed-on: https://chromium-review.googlesource.com/600530
Commit-Queue: Karl Schimpf <kschimpf@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47147}