[turbofan] Introduce separate SelectLowering reducer.

Split lowering of Select nodes into a separate graph reducer and be more
clever when lowering to diamonds, i.e. reuse diamonds that have the same
condition and only add more phis to it.

TEST=unittests
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/702463002

Cr-Commit-Position: refs/heads/master@{#25078}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25078 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix auto roll update.

Auto roll requires an additional "git fetch" now that it uses
a workdir. Before, the checkout used to be updated
externally.

BUG=408523
LOG=n
TEST=script_test.py
R=tandrii@chromium.org
TBR=tandrii@chromium.org

Review URL: https://codereview.chromium.org/695323002

Cr-Commit-Position: refs/heads/master@{#25079}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25079 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Unbreak build fon non-TF targets.

Mips64 is affected but not for long.

TEST=
BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/689113003

Cr-Commit-Position: refs/heads/master@{#25080}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25080 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: [turbofan] Also optimize unsigned division by constant.

Port r25061 (7fe697f)

TEST=cctest,mjsunit,unittests
BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/701543002

Cr-Commit-Position: refs/heads/master@{#25081}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25081 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Reland "Limit the number of transitions allowed per hidden class."

BUG=chromium:427813
LOG=N
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/676393002

Cr-Commit-Position: refs/heads/master@{#25082}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25082 ce2b1a6d-e550-0410-aec6-3dcde31c8c00