Ensure scopes are backed by blocks in the body of for loops

Ensure scopes are backed by blocks in the body of for loops

Clusterfuzz testing discovered that sloppy-mode block-scoped function
declarations introduce lexically-scoped variables in scopes that were
thrown away under the expectation that no lexically-scoped variables
were introduced. These cases are:

  for (;;) function foo() {}
  for (x in y) function foo() {}

This patch ensures that a block is created in those cases to hold the
lexically scoped variable. Usually, scope analysis should discover that
that block is not important, and it should not have a runtime
representation.

BUG=chromium:536750, chromium:536751
LOG=Y
R=adamk

Committed: https://crrev.com/2d4085622a46a700779a2e251caae8a1833c34a6
Cr-Commit-Position: refs/heads/master@{#31109}

[Dan Ehrenberg, 2015-10-02 01:31:24]

The CQ bit was checked by littledan@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-10-02 01:31:38]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1382123002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1382123002/1

[Dan Ehrenberg, 2015-10-02 01:31:38]

The CQ bit was unchecked by littledan@chromium.org

[Dan Ehrenberg, 2015-10-02 02:31:52]

The CQ bit was checked by littledan@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-10-02 02:32:07]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1382123002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1382123002/20001

[commit-bot: I haz the power, 2015-10-02 02:54:40]

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

[commit-bot: I haz the power, 2015-10-02 02:54:40]

Dry run: This issue passed the CQ dry run.

[adamk, 2015-10-05 17:41:53]

lgtm

[Dan Ehrenberg, 2015-10-05 17:54:55]

The CQ bit was checked by littledan@chromium.org

[commit-bot: I haz the power, 2015-10-05 17:55:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1382123002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1382123002/20001

[commit-bot: I haz the power, 2015-10-05 18:52:54]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-05 18:53:06]

Patchset 2 (id:??) landed as
https://crrev.com/2d4085622a46a700779a2e251caae8a1833c34a6
Cr-Commit-Position: refs/heads/master@{#31109}