Fix checked mode crash when clearing reaching type of a value.

Fix checked mode crash when clearing reaching type of a value.
When replacing uses we clear type information that is set by a previous type propagation (e.g. by CheckSmi). This led to unexpected behavior: value guarded by a CheckSmi but not Smi. Adding another type propagation pass before code generation.
Committed: https://code.google.com/p/dart/source/detail?r=20921

[srdjan, 2013-03-27 23:34:10]

Please hold off with the review, it fixed one issue but not all. Working ....

[Vyacheslav Egorov (Google), 2013-03-27 23:36:54]

I find it confusing: I thought we clear only those types that are equal to the
type definition that we are removing. If reaching type is set by CheckSmi then
it will not be equal to the type of the definition and will not be cleared.

[srdjan, 2013-03-29 20:38:59]

PTAL.

There is a discrepancy between what type is stored in the value and its
definition, therefore resetting the value type when replacing uses is not
prudent. Instead reset types of inlined LoadField only.

[Vyacheslav Egorov (Google), 2013-04-02 11:02:37]

lgtm

[srdjan, 2013-04-04 16:13:56]

Committed patchset #5 manually as r20921 (presubmit successful).