[turbofan] Turn JSContextSpecializer into an AdvancedReducer.

[turbofan] Turn JSContextSpecializer into an AdvancedReducer.

This in turn allows usage of AdvancedReducer::ReplaceWithValue which
has access to the underlying graph reducer.

R=titzer@chromium.org

Committed: https://crrev.com/ed13ea1e3227dc5b44404d54866aee466780c100
Cr-Commit-Position: refs/heads/master@{#28838}

[Benedikt Meurer, 2015-06-08 08:16:27]

bmeurer@chromium.org changed reviewers:
+ bmeurer@chromium.org

[Benedikt Meurer, 2015-06-08 08:16:27]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2015-06-08 08:16:28]

lgtm

[commit-bot: I haz the power, 2015-06-08 08:16:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1162903006/1

[commit-bot: I haz the power, 2015-06-08 09:17:48]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-08 09:17:49]

Try jobs failed on following builders:
  v8_linux_arm64_rel on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_linux_arm64_rel/builds/6392)

[Michael Starzinger, 2015-06-08 12:07:28]

The CQ bit was checked by mstarzinger@chromium.org

[Michael Starzinger, 2015-06-08 12:07:28]

The patchset sent to the CQ was uploaded after l-g-t-m from bmeurer@chromium.org
Link to the patchset: https://codereview.chromium.org/1162903006/#ps20001
(title: "Mark slow test on ARM64.")

[commit-bot: I haz the power, 2015-06-08 12:07:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1162903006/20001

[commit-bot: I haz the power, 2015-06-08 12:10:10]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-06-08 12:10:20]

Patchset 2 (id:??) landed as
https://crrev.com/ed13ea1e3227dc5b44404d54866aee466780c100
Cr-Commit-Position: refs/heads/master@{#28838}