Temporary fix for fast/events/touch/gesture/pad-gesture-fling.html crash.

The test crashes because the createFlingAnimationCurve call hits the int version in Platform.h which is no longer matching the signature in content/test/test_webkit_platform_support.h (and content/child/blink_platform_impl.h). Instead it hits the default one in Platform.h which just returns 0.
Subsequently the WebActiveGestureAnimation calls through the null pointer in WebActiveGestureAnimation::animate.

TBR=rjkroege@chromium.org, jam@chromium.org, ager@chromium.org, erik.corry@gmail.com, haraken@chromium.org, oilpan-reviews@chromium.org, tkent@chromium.org, vegorov@chromium.org, zerny@chromium.org
BUG=

Review URL: https://codereview.chromium.org/310413002

git-svn-id: svn://svn.chromium.org/blink/trunk@175493 bbb929c8-8fbe-4397-9dbb-9b2b20218538