With precise binary code coverage, the reported count is either 0 or 1.
We only report 1 the first time we collect coverage data after the
function has been executed.

Since we do not care about the accurate execution count, we can optimize
the function once it has been executed once.

Also change best effort coverage to be implicitly binary.

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

Review-Url: https://codereview.chromium.org/2766573003
Cr-Commit-Position: refs/heads/master@{#44074}