Partially revert "Ignore should-scroll-on-main-thread if main frame is not scrollable"

This partially reverts Blink r157644
(https://codereview.chromium.org/23641004), which can cause a frame
that needs to scroll on the main thread to incorrectly scroll on the
compositor thread, causing non-composited fixed position elements to
bounce around.

BUG=296823

Review URL: https://codereview.chromium.org/40373002

git-svn-id: svn://svn.chromium.org/blink/trunk@160720 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove whole include redundancies from Source directory.

There are some useless "#include" redundancies in the Source directory.
They need to be eleminated for code clean up.

BUGS=263278

Review URL: https://codereview.chromium.org/48653002

git-svn-id: svn://svn.chromium.org/blink/trunk@160721 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move AsyncFileCallbacks and friends to platform/

BUG=297477

Review URL: https://codereview.chromium.org/31933004

git-svn-id: svn://svn.chromium.org/blink/trunk@160722 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move WebCryptoAlgorithm to platform/exported/

BUG=297477

Review URL: https://codereview.chromium.org/44483002

git-svn-id: svn://svn.chromium.org/blink/trunk@160723 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Fix timeline toolbar flex layout

R=pfeldman

Review URL: https://codereview.chromium.org/47553004

git-svn-id: svn://svn.chromium.org/blink/trunk@160724 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move WebTransformKeyframe to platform/

BUG=297477

Review URL: https://codereview.chromium.org/43593005

git-svn-id: svn://svn.chromium.org/blink/trunk@160725 bbb929c8-8fbe-4397-9dbb-9b2b20218538