Eliminate remaining case of ambiguous context level info
Eliminate remaining case of ambiguous context level info

When generating the scopes in an await-for loop, make sure the scope
of the loop block is a proper sub-range of the block surrounding
the loop.

This eliminates the last case where the compiler generated context
info of the same range, but with contradicting context level info.

BUG=26941
R=regis@google.com

Review URL: https://codereview.chromium.org/2201203002 .

dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk