Revert of Change minimum length of Aura overlay scrollbars.

Revert of Change minimum length of Aura overlay scrollbars. (patchset #9 id:160001 of https://codereview.chromium.org/2734483002/ )

Reason for revert:
Unit test failing on Android: https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Android%20%28Nexus4%29/builds/62927

Original issue's description:
> Change minimum length of Aura overlay scrollbars.
> 
> It turns out Aura (and Android) overlay scrollbars weren't using the minimum
> defined in NativeThemeAura. Instead, the minimum was set from
> ScrollbarTheme::minimumThumbLength which just returns the thumb thickness.
> 
> After adding an override for ScrollbarThemeOverlay which correctly uses the
> value form NativeThemeAura, the only consumers of
> ScrollbarTheme::minimumThumbLength are the mock classes so I moved the base
> implementation into the Mock class and made the base pure virtual.
> 
> BUG=678595
> 
> Review-Url: https://codereview.chromium.org/2734483002
> Cr-Commit-Position: refs/heads/master@{#460199}
> Committed: https://chromium.googlesource.com/chromium/src/+/151a2db45f5fdbca8973988dd51d2bf6c86fbc8c

TBR=estade@chromium.org,nasko@chromium.org,pdr@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=678595
Review-Url: https://codereview.chromium.org/2780923003
Cr-Commit-Position: refs/heads/master@{#460224}
Committed: https://chromium.googlesource.com/chromium/src/+/d04d3a25c0615e015c3d8cb603ccab0081e350df

[bokan, 2017-03-28 22:23:14]

The CQ bit was checked by bokan@chromium.org

[bokan, 2017-03-28 22:23:15]

Created Revert of Change minimum length of Aura overlay scrollbars.

[commit-bot: I haz the power, 2017-03-28 22:23:51]

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, 2017-03-28 22:24:44]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1490739794800620, "parent_rev":
"dbec06a1bfb0204b72ebd11fafd0885792197043", "commit_rev":
"d04d3a25c0615e015c3d8cb603ccab0081e350df"}

[commit-bot: I haz the power, 2017-03-28 22:25:57]

Description was changed from

==========
Revert of Change minimum length of Aura overlay scrollbars. (patchset #9
id:160001 of https://codereview.chromium.org/2734483002/ )

Reason for revert:
Unit test failing on Android:
https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Andr...

Original issue's description:
> Change minimum length of Aura overlay scrollbars.
> 
> It turns out Aura (and Android) overlay scrollbars weren't using the minimum
> defined in NativeThemeAura. Instead, the minimum was set from
> ScrollbarTheme::minimumThumbLength which just returns the thumb thickness.
> 
> After adding an override for ScrollbarThemeOverlay which correctly uses the
> value form NativeThemeAura, the only consumers of
> ScrollbarTheme::minimumThumbLength are the mock classes so I moved the base
> implementation into the Mock class and made the base pure virtual.
> 
> BUG=678595
> 
> Review-Url: https://codereview.chromium.org/2734483002
> Cr-Commit-Position: refs/heads/master@{#460199}
> Committed:
https://chromium.googlesource.com/chromium/src/+/151a2db45f5fdbca8973988dd51d...

TBR=estade@chromium.org,nasko@chromium.org,pdr@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=678595
==========

to

==========
Revert of Change minimum length of Aura overlay scrollbars. (patchset #9
id:160001 of https://codereview.chromium.org/2734483002/ )

Reason for revert:
Unit test failing on Android:
https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Andr...

Original issue's description:
> Change minimum length of Aura overlay scrollbars.
> 
> It turns out Aura (and Android) overlay scrollbars weren't using the minimum
> defined in NativeThemeAura. Instead, the minimum was set from
> ScrollbarTheme::minimumThumbLength which just returns the thumb thickness.
> 
> After adding an override for ScrollbarThemeOverlay which correctly uses the
> value form NativeThemeAura, the only consumers of
> ScrollbarTheme::minimumThumbLength are the mock classes so I moved the base
> implementation into the Mock class and made the base pure virtual.
> 
> BUG=678595
> 
> Review-Url: https://codereview.chromium.org/2734483002
> Cr-Commit-Position: refs/heads/master@{#460199}
> Committed:
https://chromium.googlesource.com/chromium/src/+/151a2db45f5fdbca8973988dd51d...

TBR=estade@chromium.org,nasko@chromium.org,pdr@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=678595

Review-Url: https://codereview.chromium.org/2780923003
Cr-Commit-Position: refs/heads/master@{#460224}
Committed:
https://chromium.googlesource.com/chromium/src/+/d04d3a25c0615e015c3d8cb603cc...
==========

[commit-bot: I haz the power, 2017-03-28 22:25:58]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/d04d3a25c0615e015c3d8cb603cc...