Reapply change that makes path-observer more agressive with property lookups.

Reapply change that makes path-observer more agressive with property lookups.
Additionally fixes template-iterator to be robust in the precense of these
errors.

R=jmesserly@google.com

Committed: https://code.google.com/p/dart/source/detail?r=34456

[Siggi Cherem (dart-lang), 2014-03-26 22:36:17]

Every file that you've seen before is identical, the only new changes are in the
template_binding package.

https://codereview.chromium.org/213713002/diff/1/pkg/template_binding/test/te...
File pkg/template_binding/test/template_binding_test.dart (right):

https://codereview.chromium.org/213713002/diff/1/pkg/template_binding/test/te...
pkg/template_binding/test/template_binding_test.dart:2232: runZoned(() =>
outer.createInstance(model, new TestBindingSyntax()),
I'm not 100% convinced about having some errors being sync and some async.
Alternatively we could rework template-binding to throw and undo the changes it
was mid-way through, or finish processing the rest, but rethrow at the end of
that process. Thoughts?

[Jennifer Messerly, 2014-03-26 22:59:35]

lgtm!

(we chatted about it & think it's the best we can do for now ... any more
extensive surgery would need to be done upstream)

[Siggi Cherem (dart-lang), 2014-03-26 23:03:59]

Thanks. I added a TODO to get some of the work started to fix upstream and
removed the 'bind' from the tests as discussed

[Siggi Cherem (dart-lang), 2014-03-26 23:04:36]

Committed patchset #2 manually as r34456 (presubmit successful).