This CL moves the recording of the number of functions in a Wasm
module to the size read in the "functions" section of the module. The
advantage is that all modules read this section once, making it a good
target for collecting the data.

The previous code was also broken because in one code path, it did not
distinguish between asm.js and Wasm modules.

Bug: v8:6361
Change-Id: I6c49e91975c1730608e791036d15622d538bce77
Reviewed-on: https://chromium-review.googlesource.com/600837Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Karl Schimpf <kschimpf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47168}