[parser] Add default constructor for PreParserExpression

[parser] Add default constructor for PreParserExpression

In a few places in the parser base, we were forced to initialize
variables of type ExpressionT even if it's not necessary, as they
are assigned to later on before their use.  This was required
because, for the case of the preparser, ExpressionT is
PreParserExpression which had no default constructor.

This patch adds a default constructor, equivalent to EmptyExpression
for this class, and gets rid of the unnecessary initializations.

R=adamk@chromium.org, littledan@chromium.org
BUG=
LOG=N

Committed: https://crrev.com/6ce36869bca9a60acc77c447f7e340c3f9d1f8f2
Cr-Commit-Position: refs/heads/master@{#37884}

[nickie, 2016-07-19 09:34:50]

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

[commit-bot: I haz the power, 2016-07-19 09:35:00]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-07-19 10:08:53]

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

[commit-bot: I haz the power, 2016-07-19 10:08:53]

Dry run: This issue passed the CQ dry run.

[adamk, 2016-07-19 18:56:24]

lgtm

[nickie, 2016-07-20 07:32:02]

The CQ bit was checked by nikolaos@chromium.org

[commit-bot: I haz the power, 2016-07-20 07:32:08]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-07-20 07:34:53]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-07-20 07:35:28]

Description was changed from

==========
[parser] Add default constructor for PreParserExpression

In a few places in the parser base, we were forced to initialize
variables of type ExpressionT even if it's not necessary, as they
are assigned to later on before their use.  This was required
because, for the case of the preparser, ExpressionT is
PreParserExpression which had no default constructor.

This patch adds a default constructor, equivalent to EmptyExpression
for this class, and gets rid of the unnecessary initializations.

R=adamk@chromium.org, littledan@chromium.org
BUG=
LOG=N
==========

to

==========
[parser] Add default constructor for PreParserExpression

In a few places in the parser base, we were forced to initialize
variables of type ExpressionT even if it's not necessary, as they
are assigned to later on before their use.  This was required
because, for the case of the preparser, ExpressionT is
PreParserExpression which had no default constructor.

This patch adds a default constructor, equivalent to EmptyExpression
for this class, and gets rid of the unnecessary initializations.

R=adamk@chromium.org, littledan@chromium.org
BUG=
LOG=N

Committed: https://crrev.com/6ce36869bca9a60acc77c447f7e340c3f9d1f8f2
Cr-Commit-Position: refs/heads/master@{#37884}
==========

[commit-bot: I haz the power, 2016-07-20 07:35:28]

Patchset 1 (id:??) landed as
https://crrev.com/6ce36869bca9a60acc77c447f7e340c3f9d1f8f2
Cr-Commit-Position: refs/heads/master@{#37884}