Replace ChainContextInstr with existing IL instructions.

Replace ChainContextInstr with existing IL instructions.

v0 <- AllocateContext(...)

      ChainContext(v0)

is changed into 

v1 <- CurrentContext
      StoreField(v0.parent = v1)
      StoreContext(v0)

Since v0 is used twice, I used a TempLocalScope in
the graph builder to store the allocated context.
As a result ChainContextInstr can be completely removed
from the compiler.

R=srdjan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=25200

[Florian Schneider, 2013-07-17 12:02:12]

This is the first CL in a series to get rid of the remaining inliner bailouts
that prevent us from inlining all types of closures.

[Florian Schneider, 2013-07-18 10:45:16]

Ping.

[srdjan, 2013-07-18 16:01:26]

LGTM, thanks for the cleanup.

[Florian Schneider, 2013-07-19 09:15:37]

Committed patchset #1 manually as r25200 (presubmit successful).