X87: [turbofan] Add TruncationMode for TruncateFloat64ToInt32.

X87: [turbofan] Add TruncationMode for TruncateFloat64ToInt32.

port 4b38c15817033ccd9a65efbb3d038ae2423293c2 (r29527).

original commit message:

    We actually need round to zero truncation to implement the counterpart
    of LDoubleToI in TurboFan, which tries to convert a double to an integer
    as required for keyed load/store optimizations.

    Drive-by-cleanup: Reduce some code duplication in the InstructionSelector
    implementations.

BUG=

Committed: https://crrev.com/a02e644c50289e4a141799a4a612a3374eeb26ad
Cr-Commit-Position: refs/heads/master@{#29629}

[chunyang.dai, 2015-07-14 01:51:36]

chunyang.dai@intel.com changed reviewers:
+ weiliang.lin@intel.com

[chunyang.dai, 2015-07-14 01:51:36]

PTAL

[Weiliang, 2015-07-14 02:01:59]

The CQ bit was checked by weiliang.lin@intel.com

[Weiliang, 2015-07-14 02:01:59]

lgtm

[commit-bot: I haz the power, 2015-07-14 02:02:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1227923003/1

[commit-bot: I haz the power, 2015-07-14 02:29:50]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-14 02:30:05]

Patchset 1 (id:??) landed as
https://crrev.com/a02e644c50289e4a141799a4a612a3374eeb26ad
Cr-Commit-Position: refs/heads/master@{#29629}