Fix some clang warnings with -Wmissing-braces in v8.

Fix some clang warnings with -Wmissing-braces in v8.

Clang warns if there are missing braces around a subobject
initializer. The most common idiom that triggers this is:
  STRUCT s = {0};
if the first field of STRUCT is itself a struct. This can
be more simply written as:
  STRUCT s = {};
which also prevents the warning from firing.

BUG=chromium:505297
LOG=n

Committed: https://crrev.com/76ea6ae7445713c683369ccf5fa1e9102dd9c6b8
Cr-Commit-Position: refs/heads/master@{#29437}

[dcheng, 2015-07-01 23:29:46]

dcheng@chromium.org changed reviewers:
+ jochen@chromium.org

[jochen (gone - plz use gerrit), 2015-07-02 07:00:30]

The CQ bit was checked by jochen@chromium.org

[jochen (gone - plz use gerrit), 2015-07-02 07:00:30]

lgtm

[commit-bot: I haz the power, 2015-07-02 07:00:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1219233003/1

[commit-bot: I haz the power, 2015-07-02 07:25:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-02 07:26:06]

Patchset 1 (id:??) landed as
https://crrev.com/76ea6ae7445713c683369ccf5fa1e9102dd9c6b8
Cr-Commit-Position: refs/heads/master@{#29437}