For variables introduced as part of a catch pattern, we used to set their
"initializer position" to the beginning of the pattern.  This lead to
full-codegen eliminating crucial hole checks when reading such variables
inside the pattern itself.

R=adamk@chromium.org, littledan@chromium.org
BUG=v8:5178

Review-Url: https://codereview.chromium.org/2123953002
Cr-Commit-Position: refs/heads/master@{#37569}