We used to clear invocation counts when enabling precise coverage.
This is not necessary, and we could continue to use the existing
invocation counts on the heap. The old behavior can be achieved
by explicitly resetting the counts by polling coverage data.

R=jgruber@chromium.org,caseq@chromium.org
BUG=v8:5808

Review-Url: https://codereview.chromium.org/2768453002
Cr-Commit-Position: refs/heads/master@{#43964}