Tweak debugger safe point generation

Tweak debugger safe point generation

This change eliminates debugger safe points (DebugStepCheck calls)
on variable assignments where the value is loaded from an internal
variable.

This fixes issues like the one reported in bug 22447 by eliminating
some safe points from implicitly generated code that interfered
with user code.

To fully eliminate the root cause of this, we’d have to record the
order in which safe points on a source line are executed. That’s for
another day, month, year...

R=iposva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=44847

[hausner, 2015-04-01 22:22:18]

hausner@google.com changed reviewers:
+ iposva@google.com

[Ivan Posva, 2015-04-01 22:28:21]

LGTM -ip

[hausner, 2015-04-01 22:31:49]

Committed patchset #2 (id:20001) manually as r44847 (presubmit successful).