dart2js: Split the SimplifyInterceptors pass out from the list of optimization passes.

dart2js: Split the SimplifyInterceptors pass out from the list of optimization passes.

The backend code generator assumes that SimplifyInterceptors is alwyas
run, otherwise it will crash.  Split it out from the list of
optimizations to make it more clear that it should not be disabled.

BUG=
R=sra@google.com

Committed: https://code.google.com/p/dart/source/detail?r=44501

[Kevin Millikin (Google), 2015-03-13 10:18:03]

kmillikin@google.com changed reviewers:
+ floitsch@google.com, sra@google.com

[Kevin Millikin (Google), 2015-03-13 10:18:04]

https://codereview.chromium.org/1002213002/diff/1/pkg/compiler/lib/src/ssa/op...
File pkg/compiler/lib/src/ssa/optimize.dart (right):

https://codereview.chromium.org/1002213002/diff/1/pkg/compiler/lib/src/ssa/op...
pkg/compiler/lib/src/ssa/optimize.dart:71: // assumes it is always performed.
If this refactoring seems too aggressive, I could just commit a change that adds
this comment and nothing else (though I like the refactoring).

[sra1, 2015-03-13 12:34:09]

lgtm

[Kevin Millikin (Google), 2015-03-16 10:11:14]

Committed patchset #1 (id:1) manually as 44501 (presubmit successful).