Replace ${name} with $name where possible.

Replace ${name} with $name where possible.

...i.e. when the next character is not a part of an identifier.

R=brianwilkerson@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=41333

[Brian Wilkerson, 2014-10-27 19:21:04]

LGTM

[scheglov, 2014-10-27 19:44:02]

Committed patchset #2 (id:20001) manually as 41333 (presubmit successful).