Store pc offset instead of absolute pc in the pc descriptors.

Store pc offset instead of absolute pc in the pc descriptors.

This saves space on 64-bit platforms as the offset is stored
as a uint32_t compared to a pointer-size absolute address.

R=vegorov@google.com

Committed: https://code.google.com/p/dart/source/detail?r=43100

[Florian Schneider, 2015-01-23 10:35:39]

fschneider@google.com changed reviewers:
+ srdjan@google.com

[Vyacheslav Egorov (Google), 2015-01-23 12:00:36]

vegorov@google.com changed reviewers:
+ vegorov@google.com

[Vyacheslav Egorov (Google), 2015-01-23 12:00:36]

lgtm

[Florian Schneider, 2015-01-23 12:30:20]

Committed patchset #2 (id:20001) manually as r43100 (presubmit successful).

[srdjan, 2015-01-23 16:57:42]

lgtm