Add coalesced KeyDown handling for arrow key scrolling.

Add coalesced KeyDown handling for arrow key scrolling.

Android switched to sending coalesced KeyDown instead of
RawKeyDown/Char pair in http://crrev.com/2206053002.  The arrow key
handler in Source/web in particular did not account for this case,
therefore arrow keys stopped scrolling on Android (although all other
uses of arrow keys handled in Source/core still work).

NOTRY=true
BUG=657158
Review-Url: https://chromiumcodereview.appspot.com/2434463003
Cr-Commit-Position: refs/heads/master@{#426289}
(cherry picked from commit 5492e01d2bb022d2bdfab86250f5a4c543cea122)

Committed: https://chromium.googlesource.com/chromium/src/+/59f0841b8ba5acde00049a4fe6c27bae0cd519fa

[aelias_OOO_until_Jul13, 2016-10-19 21:53:33]

Description was changed from

==========
Add coalesced KeyDown handling for arrow key scrolling.

Android switched to sending coalesced KeyDown instead of
RawKeyDown/Char pair in http://crrev.com/2206053002.  The arrow key
handler in Source/web in particular did not account for this case,
therefore arrow keys stopped scrolling on Android (although all other
uses of arrow keys handled in Source/core still work).

NOTRY=true
BUG=657158

Review-Url: https://chromiumcodereview.appspot.com/2434463003
Cr-Commit-Position: refs/heads/master@{#426289}
(cherry picked from commit 5492e01d2bb022d2bdfab86250f5a4c543cea122)
==========

to

==========
Add coalesced KeyDown handling for arrow key scrolling.

Android switched to sending coalesced KeyDown instead of
RawKeyDown/Char pair in http://crrev.com/2206053002.  The arrow key
handler in Source/web in particular did not account for this case,
therefore arrow keys stopped scrolling on Android (although all other
uses of arrow keys handled in Source/core still work).

NOTRY=true
BUG=657158

Review-Url: https://chromiumcodereview.appspot.com/2434463003
Cr-Commit-Position: refs/heads/master@{#426289}
(cherry picked from commit 5492e01d2bb022d2bdfab86250f5a4c543cea122)

Committed:
https://chromium.googlesource.com/chromium/src/+/59f0841b8ba5acde00049a4fe6c2...
==========

[aelias_OOO_until_Jul13, 2016-10-19 21:53:34]

Committed patchset #1 (id:1) manually as
59f0841b8ba5acde00049a4fe6c27bae0cd519fa.