We only report the usages when full parse is happening, i.e. only when the function that declares a legacy const is compiled. This is an approximation that is easy to implement, but still should reflect the real-world usage.

BUG=v8:3942
LOG=N

Review URL: https://codereview.chromium.org/1041863002

Cr-Commit-Position: refs/heads/master@{#27526}