Narrow bisect:
https://chromium.googlesource.com/chromium/src/+log/57ad17882fe82d222ffc20d8d03140c1afa366a8..a6293982c7f5c0ad0e2ae56238fd6062ca866fcf?pretty=fuller&n=10

Suspecting: r383663 ?

Could you please help me to reassign this issue if your change is not cause for it?

Note:1. Above issue is found on chromium build (i.e. TOT)
     2. Will soon update the Linux info.

P.S: This was tested on chromium TOT build 51.0.2694.0 (Developer Build) 15f9964b8ff56961f10d34bf39715a5cc457f869-refs/heads/master@{#383698} 

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

 Issue 599057  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1f6dc1b24dfb56e0199b851f1c121195e33f2bd6

commit 1f6dc1b24dfb56e0199b851f1c121195e33f2bd6
Author: dtapuska <dtapuska@chromium.org>
Date: Wed Mar 30 20:39:40 2016

Fix mouse wheel scrolling on PDFs.

With the fix for flash not receiving wheel events
(see https://codereview.chromium.org/1828203003/) this broke PDFs
scrolling since they do want the events but then the events get
resent. When the events were resent they didn't have the appropriate
canScroll set on them causing gestures not to be generate.

Do not conflate canScroll in the mouse wheel event queue
to prevent the default action in blink. Just plumb
it via a WebSetting instead. This setting will eventually
be removed when the default wheel event path is removed.

BUG= 598658 

Review URL: https://codereview.chromium.org/1841053002

Cr-Commit-Position: refs/heads/master@{#384081}

[modify] https://crrev.com/1f6dc1b24dfb56e0199b851f1c121195e33f2bd6/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
[modify] https://crrev.com/1f6dc1b24dfb56e0199b851f1c121195e33f2bd6/content/browser/renderer_host/render_widget_host_view_aura_unittest.cc
[modify] https://crrev.com/1f6dc1b24dfb56e0199b851f1c121195e33f2bd6/content/renderer/render_view_impl.cc
[modify] https://crrev.com/1f6dc1b24dfb56e0199b851f1c121195e33f2bd6/third_party/WebKit/Source/core/frame/Settings.in
[modify] https://crrev.com/1f6dc1b24dfb56e0199b851f1c121195e33f2bd6/third_party/WebKit/Source/core/input/EventHandler.cpp
[modify] https://crrev.com/1f6dc1b24dfb56e0199b851f1c121195e33f2bd6/third_party/WebKit/Source/web/WebSettingsImpl.cpp
[modify] https://crrev.com/1f6dc1b24dfb56e0199b851f1c121195e33f2bd6/third_party/WebKit/Source/web/WebSettingsImpl.h
[modify] https://crrev.com/1f6dc1b24dfb56e0199b851f1c121195e33f2bd6/third_party/WebKit/Source/web/WebViewImpl.cpp
[modify] https://crrev.com/1f6dc1b24dfb56e0199b851f1c121195e33f2bd6/third_party/WebKit/Source/web/WebViewImpl.h
[modify] https://crrev.com/1f6dc1b24dfb56e0199b851f1c121195e33f2bd6/third_party/WebKit/public/web/WebSettings.h