When separating compile from instantiation, I accidentally elided size
reporting for wasm functions. This change fixes that (verified with
re-running benchmarks), and also consolidates the responsibility of
size reporting within the instantiation method, away from the various
compile phases.

We should probably rethink this reporting when we move wasm codegen
off the JS Heap, if the wasm module code ends up being shared.

BUG=

Review-Url: https://codereview.chromium.org/2079353002
Cr-Commit-Position: refs/heads/master@{#37120}