Revert of Cleanup and unify Isolate::ReportPendingMessages. (patchset #4 id:60001 of https://codereview.chromium.org/999923004/)

Reason for revert:
Failing Blink tests on Win and Mac:
- plugins/netscape-plugin-property-access-exception.html
- http/tests/plugins/cross-frame-object-access.html

Original issue's description:
> Cleanup and unify Isolate::ReportPendingMessages.
>
> Note that this is a pure cleanup CL and shouldn't have an observable
> impact on the functional behavior of message reporting.
>
> R=yangguo@chromium.org

TBR=yangguo@chromium.org,machenbach@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1016323002

Cr-Commit-Position: refs/heads/master@{#27306}