Fix main intent metrics when zero tabs present.

Fix main intent metrics when zero tabs present.

The previous ignore logic was incorrect as it was both calling
create and set index.  Thus the zero tabs case was resulting in
switch tabs always.

Adds tests to catch regressions going forward.

BUG=717062
Review-Url: https://codereview.chromium.org/2850163002
Cr-Original-Commit-Position: refs/heads/master@{#468493}
Review-Url: https://codereview.chromium.org/2880253003 .
Cr-Commit-Position: refs/branch-heads/3071@{#565}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed: https://chromium.googlesource.com/chromium/src/+/b9958d0e3c2b58bd8992b5a1eb47d8d1a65428fe

[Ted C, 2017-05-15 20:26:01]

Description was changed from

==========
Fix main intent metrics when zero tabs present.

The previous ignore logic was incorrect as it was both calling
create and set index.  Thus the zero tabs case was resulting in
switch tabs always.

Adds tests to catch regressions going forward.

BUG=717062

Review-Url: https://codereview.chromium.org/2850163002
Cr-Commit-Position: refs/heads/master@{#468493}
(cherry picked from commit 7fb9cb4281ac50effd7bdb628e6737fb2d518c4e)
==========

to

==========
Fix main intent metrics when zero tabs present.

The previous ignore logic was incorrect as it was both calling
create and set index.  Thus the zero tabs case was resulting in
switch tabs always.

Adds tests to catch regressions going forward.

BUG=717062

Review-Url: https://codereview.chromium.org/2850163002
Cr-Original-Commit-Position: refs/heads/master@{#468493}
Review-Url: https://codereview.chromium.org/2880253003 .
Cr-Commit-Position: refs/branch-heads/3071@{#565}
Cr-Branched-From:
a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed:
https://chromium.googlesource.com/chromium/src/+/b9958d0e3c2b58bd8992b5a1eb47...
==========

[Ted C, 2017-05-15 20:26:02]

Committed patchset #1 (id:1) manually as
b9958d0e3c2b58bd8992b5a1eb47d8d1a65428fe.