Fix invalid read of language mode from StorePropertyParameters.

Fix invalid read of language mode from StorePropertyParameters.

Fixes an invalid cast of an Operator1<StorePropertyParameters> object
to Operator1<LanguageMode> by reading the language mode from
StorePropertyParameters. This code happened to work before because
StorePropertyParameters's first field has type LanguageMode.

Cleanup for cfi_vptr=1; see https://www.chromium.org/developers/testing/control-flow-integrity

BUG=chromium:457523
R=bmeurer@chromium.org
LOG=N

Committed: https://crrev.com/718fc1c9a24d3870220ff19a85b226a66fb3a17b
Cr-Commit-Position: refs/heads/master@{#30493}

[Benedikt Meurer, 2015-09-01 04:03:34]

LGTM

[pcc1, 2015-09-01 04:16:46]

The CQ bit was checked by pcc@chromium.org

[commit-bot: I haz the power, 2015-09-01 04:16:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1311393008/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1311393008/1

[commit-bot: I haz the power, 2015-09-01 05:05:07]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-01 05:05:20]

Patchset 1 (id:??) landed as
https://crrev.com/718fc1c9a24d3870220ff19a85b226a66fb3a17b
Cr-Commit-Position: refs/heads/master@{#30493}