Reapply "Add a shrinking reduction for dead continuation parameters."

Reapply "Add a shrinking reduction for dead continuation parameters."

This reapplies SVN revision r43093 with bug fixes.  A failing assert
was fixed, and continuation eta-reduction was restricted to not change
non-call continuations into call continuations.  If these were to
occur, they risk duplicating code and so are not always on
optimization.

BUG=
R=asgerf@google.com

Committed: https://code.google.com/p/dart/source/detail?r=43135

[Kevin Millikin (Google), 2015-01-26 11:25:57]

kmillikin@google.com changed reviewers:
+ asgerf@google.com

[Kevin Millikin (Google), 2015-01-26 11:25:58]

Reapply this while disallowing continuation eta-reduction that turns a non-call
continuation into a call continuation (i.e., that uses a non-call continuation
as a call continuation).

[Kevin Millikin (Google), 2015-01-26 11:26:17]

The fix is in the diff from patch set 1 -> 2.

[asgerf, 2015-01-26 12:56:57]

Still LGTM

https://codereview.chromium.org/872373003/diff/20001/pkg/compiler/lib/src/cps...
File pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart (right):

https://codereview.chromium.org/872373003/diff/20001/pkg/compiler/lib/src/cps...
pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart:290: // Do not perform
reductions replace a function call continuation with a
*that* replace or *replacing*

[Kevin Millikin (Google), 2015-01-26 13:51:50]

Committed patchset #2 (id:20001) manually as 43135 (presubmit successful).