Revert "Refactoring animation code in accelerated path."

We are currently crashing at an ASSERT_NOT_REACHED in
WebAnimationProvider.cpp(61). Reverting while we investigate.

This reverts commit e283c73dcea8ef7f5f4a9d4634cd168d5ef9a97f.

TBR=dongseong.hwang
BUG=None

Review URL: https://codereview.chromium.org/24239011

git-svn-id: svn://svn.chromium.org/blink/trunk@158137 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert r158059 - "Add code style check error for using static_cast instead of toFoo function."

I think this change broke test-webkitpy on WinXP, and the change had other
implementation flaws I noticed on further review :(. See comments on the
original CL ( https://chromiumcodereview.appspot.com/23654034/ ) for more.

TBR=r.kasibhatla@samsung.com, eseidel@chromium.org, inferno@chromium.org
BUG=

Review URL: https://codereview.chromium.org/23792011

git-svn-id: svn://svn.chromium.org/blink/trunk@158138 bbb929c8-8fbe-4397-9dbb-9b2b20218538