Correction:
Actual: Scroll bar bounces back after scrolling page up/down for pdf file.

Expected: Scroll bar should work smoothly after scrolling page up/down for pdf file.

Manual regression range:
Good Build: 51.0.2686.0
Bad Build:  51.0.2687.0

Narrow bisect:
https://chromium.googlesource.com/chromium/src/+log/6bebadddb399ad1c1f91592efed410040617e708..5840ac85a7c912d9ddb764007b6a9ec65a26ad22?pretty=fuller&n=30

Suspecting: 382345 ?
Kindly help to re-assign, if your changes are not cause for this issue.

Note: Issue not seen on Win & Linux OS.

Deleted: Actual_Scroll.mov 2.5 MB

Actual_Scroll.mov 2.5 MB Download

Adding release block label, please undo if not the case.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c1d91e8f7cd46f1cb68ec09e49d4de5c90175d6c

commit c1d91e8f7cd46f1cb68ec09e49d4de5c90175d6c
Author: dtapuska <dtapuska@chromium.org>
Date: Wed Mar 23 19:34:51 2016

Fix missing fields in GestureScrollBegin/Update/End event conversions.

Some of the fields were missing from the event conversion path that
occurs when a plugin is used. This caused fields to be populated
with the default value. As a result the default values enabled
overscroll scrolling when using a low precision delta
mouse wheel with an MacOSX machine.

The bug did not indicate which precision of mouse was being
used but overscrolling for PDF files with a touchpad or a magic
mouse (which have high precision deltas) still enable
elastic overscroll; but that is consistent with MacOSX.
This is a behavioural change for MacOSX but is consistent
with Safari when using a high precision mouse.

BUG= 596778 

Review URL: https://codereview.chromium.org/1829743003

Cr-Commit-Position: refs/heads/master@{#382901}

[modify] https://crrev.com/c1d91e8f7cd46f1cb68ec09e49d4de5c90175d6c/third_party/WebKit/Source/core/events/GestureEvent.cpp
[modify] https://crrev.com/c1d91e8f7cd46f1cb68ec09e49d4de5c90175d6c/third_party/WebKit/Source/core/events/GestureEvent.h
[modify] https://crrev.com/c1d91e8f7cd46f1cb68ec09e49d4de5c90175d6c/third_party/WebKit/Source/platform/PlatformGestureEvent.h
[modify] https://crrev.com/c1d91e8f7cd46f1cb68ec09e49d4de5c90175d6c/third_party/WebKit/Source/web/WebInputEventConversion.cpp
[modify] https://crrev.com/c1d91e8f7cd46f1cb68ec09e49d4de5c90175d6c/third_party/WebKit/Source/web/tests/WebInputEventConversionTest.cpp

This is fixed for non high precision mouse wheels.

If you use a touchpad it will animate overscroll much like everything else does in MacOSX.