Add comment for the forked Dart revision for the assembler code.

Add comment for the forked Dart revision for the assembler code.

Also note to keep that up to date.
See also Patch set 1 of https://codereview.chromium.org/574133002/,
vs later patch sets.

Some things that were changed:
(*) Headers / constants use Ice version (RegX8632::Encoded_Reg_eax vs EAX), (KB / MB -> other...)
(*) Use llvm/Subzero allocator instead of Dart one.
(*) Class/Field/On-stack-replacement/Dart runtime stuff is removed
(*) Relocation/Fixups are now POD -- rather than a class
with a virtual method for fixup. For now, we write out
an ELF relocation, but later we may do a target pass
to handle function calls within the same section, etc.
(*) ASSERT -> assert
(*) uword -> uintptr_t (should check).
(*) clang-format
(*) ???

BUG=none
R=stichnot@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=33a5f41d1e1224bdc8dab1fd1f2834281331df40

[jvoung (off chromium), 2015-02-03 21:32:52]

jvoung@chromium.org changed reviewers:
+ shyamsundarr@chromium.org, stichnot@chromium.org

[Jim Stichnoth, 2015-02-03 21:44:50]

lgtm

https://codereview.chromium.org/901453002/diff/1/src/assembler.cpp
File src/assembler.cpp (right):

https://codereview.chromium.org/901453002/diff/1/src/assembler.cpp#newcode8
src/assembler.cpp:8: // This is forked from Dart revision 39313.
Would it be too hand-holdy to reference something like
https://code.google.com/p/dart/wiki/GettingTheSource ?

[jvoung (off chromium), 2015-02-03 23:07:16]

New patchsets have been uploaded after l-g-t-m from stichnot@chromium.org

[jvoung (off chromium), 2015-02-03 23:09:09]

https://codereview.chromium.org/901453002/diff/1/src/assembler.cpp
File src/assembler.cpp (right):

https://codereview.chromium.org/901453002/diff/1/src/assembler.cpp#newcode8
src/assembler.cpp:8: // This is forked from Dart revision 39313.
On 2015/02/03 21:44:50, stichnot wrote:
> Would it be too hand-holdy to reference something like
> https://code.google.com/p/dart/wiki/GettingTheSource ?

Done. I was a little afraid of the link going stale, but it's probably fine.

[jvoung (off chromium), 2015-02-04 00:06:48]

Committed patchset #2 (id:20001) manually as
33a5f41d1e1224bdc8dab1fd1f2834281331df40 (presubmit successful).