Reduce allocation size of FormData::m_entries.

Reduce allocation size of FormData::m_entries.

Store Entry objects as pointers instead of inline objects.  This reduces the
size of unused slots in m_entries Vector.
Also, FormData::Entry no longer need to support copy operations.  It's immutable
now.

This CL has no user-visible behavior changes.

BUG=528840
R=keishi@chromium.org

Committed: https://crrev.com/4f4e4604d866331ae8c6ce04becf81fe10b3ae34
git-svn-id: svn://svn.chromium.org/blink/trunk@202172 bbb929c8-8fbe-4397-9dbb-9b2b20218538

[tkent, 2015-09-14 00:48:46]

Patchset #1 (id:1) has been deleted

[tkent, 2015-09-14 01:27:44]

tkent@chromium.org changed reviewers:
+ keishi@chromium.org

[tkent, 2015-09-14 01:27:44]

Keishi, please review this.

[keishi, 2015-09-14 02:36:49]

LGTM

[tkent, 2015-09-14 03:07:20]

The CQ bit was checked by tkent@chromium.org

[commit-bot: I haz the power, 2015-09-14 03:07:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1338193002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1338193002/20001

[tkent, 2015-09-14 04:22:27]

Committed patchset #1 (id:20001) manually as 202172 (presubmit successful).

[commit-bot: I haz the power, 2015-09-23 12:28:56]

Patchset 1 (id:??) landed as
https://crrev.com/4f4e4604d866331ae8c6ce04becf81fe10b3ae34