Remove *RowHeightScrollHelper from scroll_view.h/cc

Remove *RowHeightScrollHelper from scroll_view.h/cc

These classes are not currently in use anywhere. They were part of the
initial.commit from 2008 so it's hard to tell why they might have been
added originally.

BUG=none

[Evan Stade, 2016-11-17 01:18:46]

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

[commit-bot: I haz the power, 2016-11-17 01:20:28]

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, 2016-11-17 03:22:51]

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

[commit-bot: I haz the power, 2016-11-17 03:22:52]

Dry run: Try jobs failed on following builders:
  android_arm64_dbg_recipe on master.tryserver.chromium.android (JOB_TIMED_OUT,
no build URL)
  android_clang_dbg_recipe on master.tryserver.chromium.android (JOB_TIMED_OUT,
no build URL)
  android_compile_dbg on master.tryserver.chromium.android (JOB_TIMED_OUT, no
build URL)
  android_cronet on master.tryserver.chromium.android (JOB_TIMED_OUT, no build
URL)
  cast_shell_android on master.tryserver.chromium.android (JOB_TIMED_OUT, no
build URL)

[Evan Stade, 2016-11-17 18:11:51]

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

[Evan Stade, 2016-11-17 18:11:56]

estade@chromium.org changed reviewers:
+ sky@chromium.org

[commit-bot: I haz the power, 2016-11-17 18:12:43]

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, 2016-11-17 19:22:35]

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

[commit-bot: I haz the power, 2016-11-17 19:22:36]

Dry run: This issue passed the CQ dry run.

[sky, 2016-11-17 20:08:58]

These were used to handle scrolling by lines. I actually think we should keep
this code and it should be hooked up to the task manager. That way clicking the
scroll by line button would treat groups of tabs in the same process as a single
scroll.

[Evan Stade, 2016-11-17 21:13:49]

ok, filed bug 666464. Closing this CL.