Replace the current contiguity check for composited scrolling

LayoutTests/TestExpectations

 # See http://trac.webkit.org/wiki/TestExpectations for more information on this file.
 
 # -----------------------------------------------------------------
 # SLOW TESTS
 # -----------------------------------------------------------------
 
 crbug.com/24182 [ Debug ] css3/flexbox/multiline-justify-content.html [ Slow ]
 webkit.org/b/91666 [ Mac ] editing/input/emacs-ctrl-o.html [ Failure Slow ]
 webkit.org/b/91666 [ Mac ] editing/pasteboard/emacs-ctrl-k-y-001.html [ Failure Slow ]
 webkit.org/b/91666 [ Mac ] editing/pasteboard/emacs-ctrl-a-k-y.html [ Failure Slow ]
@@ skipping 2375 matching lines @@
 webkit.org/b/92968 http/tests/appcache/abort-cache-onchecking-manifest-404.html
 webkit.org/b/92968 http/tests/appcache/abort-cache-onchecking-resource-404.html
 webkit.org/b/92968 http/tests/appcache/abort-cache-ondownloading-resource-404.html
 webkit.org/b/92968 http/tests/appcache/abort-cache-onchecking.html
 webkit.org/b/92968 http/tests/appcache/abort-cache-ondownloading.html
 webkit.org/b/92968 http/tests/appcache/abort-cache-onprogress.html
 
 # Scrolling content draws beneath scrollbars in composited scrolling mode.
 webkit.org/b/103156 virtual/gpu/compositedscrolling/scrollbars/custom-scrollbar-with-incomplete-style.html [ ImageOnlyFailure ]
 
-# Adding new failing layout tests to illustrate the need for a future logic fix.
-# Will be fixed in upcoming patch.
-crbug.com/172875 compositing/overflow/automatically-opt-into-composited-scrolling.html [ Failure ]
-crbug.com/172875 compositing/overflow/opt-into-composited-scrolling-positioned-ancestor.html [ Failure ]
-crbug.com/172875 virtual/gpu/compositedscrolling/overflow/automatically-opt-into-composited-scrolling.html [ Failure ]
-crbug.com/172875 virtual/gpu/compositedscrolling/overflow/opt-into-composited-scrolling-positioned-ancestor.html [ Failure ]
-crbug.com/172875 virtual/softwarecompositing/overflow/automatically-opt-into-composited-scrolling.html [ Failure ]
-crbug.com/172875 virtual/softwarecompositing/overflow/opt-into-composited-scrolling-positioned-ancestor.html [ Failure ]
-
 # Will need updated baselines with the opt-in fixes.
 crbug.com/234482 [ Linux Win Mac ] virtual/gpu/compositedscrolling/overflow/overflow-scroll.html [ Failure ]
 
 # Fails due to Bug 85856.
 webkit.org/b/85856 [ Win Mac ] fast/block/float/028.html [ ImageOnlyFailure ]
 webkit.org/b/85856 [ Win Mac ] fast/block/float/026.html [ ImageOnlyFailure ]
 webkit.org/b/85856 [ Win Mac ] fast/overflow/unreachable-overflow-rtl-bug.html [ Failure ImageOnlyFailure ]
 webkit.org/b/85856 [ Linux Win SnowLeopard ] scrollbars/rtl/div-absolute.html [ Failure ]
 webkit.org/b/85856 [ Linux Win SnowLeopard ] virtual/gpu/compositedscrolling/scrollbars/rtl/div-absolute.html [ Failure ]
 webkit.org/b/85856 [ Lion MountainLion ] scrollbars/rtl/div-absolute.html [ Failure Pass ]
@@ skipping 668 matching lines @@
 crbug.com/234066 fast/dom/everything-to-string.html [ Pass Failure ]
 crbug.com/234069 [ Mac Release ] fast/events/touch/gesture/long-press-drag-drop-touch-editing-combined.html [ Pass Failure ]
 
 crbug.com/234555 [ Debug ] fast/ruby/ruby-svg-crash.html [ Failure ]
 
 crbug.com/234891 fast/dom/timer-throttling-hidden-page.html [ Pass Failure ]
 
 crbug.com/234758 [ Mac Debug ] http/tests/security/isolatedWorld/all-window-prototypes.html [ Failure Timeout Pass ]
 crbug.com/234758 [ Debug ] fast/workers/worker-document-leak.html [ Pass Timeout ]
 crbug.com/234758 webaudio/audiobuffersource-multi-channels.html [ Pass Crash ]