[turbofan] Debug-time helpers for regalloc data structures

When working on the register allocator, I often need to introspect the various components of the model - e.g. InstructionSequence, Instruction, LiveRange, etc. A pretty printer would help. While we have a suite of operator<< defined for these types, turns out that using them at debug time is close to impossible - gdb has poor (or convoluted) support for instantiating structures (e.g. OFStream, PrintableInstructionSequence, etc), and calling operator<< with pass-by-reference semantics.

I explored gdb macros, but hit an issue quite early with instantiating and initializing an OFStream - "virtual baseclass botch".

Currently, I have a side-file that I include (and then remove before publishing CLs), which defines wrappers to the above operator<< APIs, but this is becoming quite awkward, and I believe the functionality to be quite useful to anyone working in this (regalloc) area, so it's worth having something better than local side-files. The gdb path seems overly-twisted for the problem at hand, and I've noticed elsewhere (e.g. Object) the presence of Print APIs - hence this change.

BUG=

Committed: https://crrev.com/ee005fbb8112d8ee55b4d139a5b1996cede1ea5f
Cr-Commit-Position: refs/heads/master@{#30039}

[Mircea Trofin, 2015-08-05 23:14:35]

mtrofin@chromium.org changed reviewers:
+ bmeurer@chromium.org, jarin@chromium.org

[Mircea Trofin, 2015-08-05 23:15:03]

Re-opening the topic of pretty printers for regalloc data structures at debug
time.

[Jarin, 2015-08-06 05:47:28]

lgtm

[Mircea Trofin, 2015-08-06 06:13:40]

The CQ bit was checked by mtrofin@chromium.org

[commit-bot: I haz the power, 2015-08-06 06:13:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1280483002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1280483002/1

[commit-bot: I haz the power, 2015-08-06 06:15:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-06 06:15:43]

Patchset 1 (id:??) landed as
https://crrev.com/ee005fbb8112d8ee55b4d139a5b1996cede1ea5f
Cr-Commit-Position: refs/heads/master@{#30039}