Don't update the title to about:blank on first show for custom tabs

Don't update the title to about:blank on first show for custom tabs

Currently custom tabs don't show a title if the title is still the url,
but due to optimizations inside warmup(), the title might end up being
about:blank (even if the current url is not about:blank). The domain
explicitly guards against this but title doesn't. Update the title to
also never show about:blank

BUG=579647
Committed: https://chromium.googlesource.com/chromium/src/+/3cf7fe595ce982437a875af505f4750b9309c435

[Yusuf, 2016-01-29 23:32:00]

Description was changed from

==========
Don't update the title to about:blank on first show for custom tabs

Currently custom tabs don't show a title if the title is still the url,
but due to optimizations inside warmup(), the title might end up being
about:blank (even if the current url is not about:blank). The domain
explicitly guards against this but title doesn't. Update the title to
also never show about:blank

BUG=579647
==========

to

==========
Don't update the title to about:blank on first show for custom tabs

Currently custom tabs don't show a title if the title is still the url,
but due to optimizations inside warmup(), the title might end up being
about:blank (even if the current url is not about:blank). The domain
explicitly guards against this but title doesn't. Update the title to
also never show about:blank

BUG=579647

Committed:
https://chromium.googlesource.com/chromium/src/+/3cf7fe595ce982437a875af505f4...
==========

[Yusuf, 2016-01-29 23:32:04]

Committed patchset #1 (id:1) manually as
3cf7fe595ce982437a875af505f4750b9309c435.