There are two break locations at the same source location by desugaring:
- call iterator.next,
- before variable assignment.

Additionally location for for..of loops is moved from before "of" to before each variable expression.

We should not report first implicit call to avoid user confusion. User still able to go into .next function with both scenarios:
- when this call is reached by stepOver or stepInto from previous line,
- when this call is reached because of breakpoint at current line.

BUG=v8:6425
R=dgozman@chromium.org,jgruber@chromium.org

Review-Url: https://codereview.chromium.org/2893313002
Cr-Commit-Position: refs/heads/master@{#45509}