Fix register allocation bug in building use intervals.

Fix register allocation bug in building use intervals.

This bug was only exposed on ARM, but can be a problem
on other platforms as well.

When building the use intervals for a value that
is used more than once at one instruction, the use
interval was not adjusted correctly: Under certain
conditions the resulting interval can be too short.
It can occur when the first use is a writable register use,
and the second use is a normal register use.
This CL grows the use intervals to the correct size
in that case.

BUG=https://code.google.com/p/dart/issues/detail?id=11800
TEST=tests/language/regress_11800_test.dart
R=vegorov@google.com

Committed: https://code.google.com/p/dart/source/detail?r=25810

[Vyacheslav Egorov (Google), 2013-08-06 12:31:32]

lgtm

[Florian Schneider, 2013-08-06 12:43:13]

Committed patchset #1 manually as r25810 (presubmit successful).