tuple: leave fields uninitialized in default constructors

tuple: leave fields uninitialized in default constructors

Using "x()" in TupleLeaf's default constructor causes primitive types
(e.g., integers and pointers) to be zero initialized, whereas
previously Tuple left them indeterminate.  Arguably zero-initializing
is better, but the change was inadvertant and results in a measurable
code size increase, so this CL reverts it (at least for now).

BUG=440806
Committed: https://crrev.com/f2c5add463f5fbb425934ef71390ca848a9df01a
Cr-Commit-Position: refs/heads/master@{#308455}

[mdempsky, 2014-12-15 21:36:59]

mdempsky@chromium.org changed reviewers:
+ thakis@chromium.org

[Nico, 2014-12-15 21:37:58]

lgtm, thanks!

[mdempsky, 2014-12-15 21:55:24]

The CQ bit was checked by mdempsky@chromium.org

[commit-bot: I haz the power, 2014-12-15 21:56:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/791883003/20001

[commit-bot: I haz the power, 2014-12-15 23:26:21]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-12-15 23:27:18]

Patchset 2 (id:??) landed as
https://crrev.com/f2c5add463f5fbb425934ef71390ca848a9df01a
Cr-Commit-Position: refs/heads/master@{#308455}