Restore the "don't flatten scrolling content layer" logic.

LayoutTests/TestExpectations

 crbug.com/504613 paint/images/image-backgrounds-not-antialiased.html [ ImageOnlyFailure ]
 crbug.com/502531 fast/borders/border-antialiasing.html [ ImageOnlyFailure ]
 
 crbug.com/417782 [ Linux Win ] virtual/rootlayerscrolls/fast/scrolling/fractional-scroll-offset-fixed-position-non-composited.html [ ImageOnlyFailure ]
 crbug.com/449242 [ Linux ] fast/css/word-spacing-characters-complex-text.html [ ImageOnlyFailure ]
 crbug.com/492664 [ Linux XP ] imported/csswg-test/css-writing-modes-3/box-offsets-rel-pos-vlr-005.xht [ ImageOnlyFailure ]
 crbug.com/492664 [ Linux XP ] imported/csswg-test/css-writing-modes-3/box-offsets-rel-pos-vrl-004.xht [ ImageOnlyFailure ]
 crbug.com/492664 [ Mac ] imported/csswg-test/css-writing-modes-3/bidi-embed-002.html [ ImageOnlyFailure ]
 crbug.com/492664 [ Mac ] imported/csswg-test/css-writing-modes-3/bidi-isolate-002.html [ ImageOnlyFailure ]
 crbug.com/492664 [ Win ] imported/csswg-test/css-writing-modes-3/bidi-override-005.html [ ImageOnlyFailure ]
@@ skipping 646 matching lines @@
 
 crbug.com/443382 imported/web-platform-tests/subresource-integrity/subresource-integrity.html [ Failure Timeout ]
 
 crbug.com/396775 compositing/overflow/reflected-overlay-scrollbars-should-appear-without-compositing.html [ ImageOnlyFailure ]
 crbug.com/396775 virtual/prefer_compositing_to_lcd_text/compositing/overflow/reflected-overlay-scrollbars-should-appear-without-compositing.html [ ImageOnlyFailure ]
 
 crbug.com/381684 [ Win Android Mac ] fonts/family-fallback-gardiner.html [ Skip ]
 
 crbug.com/467635 fast/dom/HTMLImageElement/image-sizes-meta-viewport.html [ Skip ]
 
+crbug.com/521768 compositing/layer-creation/fixed-position-in-fixed-overflow.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/layer-creation/fixed-position-nonscrollable-body-mismatch-containers.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/clear-scroll-parent.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/composited-scrolling-paint-phases.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/content-gains-scrollbars.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/overflow-scrollbar-layers.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/reparented-scrollbars-non-sc-anc.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/scroll-parent-absolute.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/scroll-parent-with-non-stacking-context-composited-ancestor.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/scrolling-content-clip-to-viewport.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/scrolling-without-painting.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/selection-gaps-after-removing-scrolling-contents.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/selection-gaps-toggling-with-scrolling-contents.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/selection-gaps-toggling.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/textarea-scroll-touch.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/universal-accelerated-overflow-scroll.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/overflow/updating-scrolling-content.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/repaint/should-not-clip-composited-overflow-scrolling-layer.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/scrollbars/nested-overlay-scrollbars.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/squashing/composited-bounds-for-negative-z.html [ NeedsRebaseline ]
+crbug.com/521768 compositing/update-paint-phases.html [ NeedsRebaseline ]
+crbug.com/521768 fast/repaint/overflow-move-after-scroll.html [ NeedsRebaseline ]
+crbug.com/521768 fast/repaint/overflow-scroll-after-move.html [ NeedsRebaseline ]
+crbug.com/521768 paint/invalidation/invalidate-after-composited-scroll.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/clear-scroll-parent.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/composited-scrolling-paint-phases.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/content-gains-scrollbars.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/overflow-auto-with-touch-toggle.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/overflow-auto-with-touch.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/overflow-overlay-with-touch.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/overflow-scrollbar-layers.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/reparented-scrollbars-non-sc-anc.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/scroll-parent-absolute.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/scroll-parent-with-non-stacking-context-composited-ancestor.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/scrolling-content-clip-to-viewport.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/scrolling-without-painting.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/selection-gaps-after-removing-scrolling-contents.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/selection-gaps-toggling-with-scrolling-contents.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/selection-gaps-toggling.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/text-color-change.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/text-match-highlight.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/textarea-scroll-touch.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/universal-accelerated-overflow-scroll.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/updating-scrolling-container-and-content.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/updating-scrolling-container.html [ NeedsRebaseline ]
+crbug.com/521768 virtual/prefer_compositing_to_lcd_text/compositing/overflow/updating-scrolling-content.html [ NeedsRebaseline ]
+
 crbug.com/517898 [ SnowLeopard Debug ] fast/text/international/bidi-neutral-run.html [ Crash ]
 
 # crbug.com/396823 [ Mac ] fast/multicol/multicol-with-child-renderLayer-for-input.html [ ImageOnlyFailure ]
 
 crbug.com/484370 [ Win Debug ] svg/custom/gradient-userSpaceOnUse-with-percentage.svg [ ImageOnlyFailure ]
 
 crbug.com/116710 [ Win Debug ] transforms/3d/point-mapping/3d-point-mapping-preserve-3d.html [ ImageOnlyFailure ]
 
 # Printing Layout broken in these tests.
 crbug.com/377696 printing/setPrinting.html [ Skip ]
@@ skipping 300 matching lines @@
 
 # Yosemite-specific failures that still need triaging.
 # Form controls need rebaseline because of the default font change.
 # If you see wider INPUT elements or narrower TEXTAREA elements, you may do just
 # rebaseline. See crbug.com/508768#c6
 crbug.com/509025 [ Yosemite ] compositing/layer-creation/compositing-reason-removed.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/layer-creation/should-invoke-deferred-compositing.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/overflow/fixed-scroll-in-empty-root-layer.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/overflow/text-color-change.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/overflow/text-match-highlight.html [ Failure ]
-crbug.com/509025 [ Yosemite ] compositing/overflow/textarea-scroll-touch.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/overflow/updating-scrolling-container-and-content.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/overflow/updating-scrolling-container.html [ Failure ]
 # TODO(chrishtr): uncomment/inspect rebaseline of this after fixing crbug.com/516016
 # crbug.com/509025 [ Yosemite ] compositing/repaint/should-not-clip-composited-overflow-scrolling-layer.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/squashing/iframe-inside-squashed-layer.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/squashing/invalidate-when-leaving-squashed-layer.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/squashing/invalidation-for-subpixel-offset-of-squashed-layer.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/squashing/invalidations-with-large-negative-margin.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/squashing/remove-squashed-layer-plus-move.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/squashing/repaint-overflow-scrolled-squashed-content.html [ Failure ]
@@ skipping 19 matching lines @@
 crbug.com/509025 [ Yosemite ] fast/text/missing-glyph-in-combining-character-sequence.html [ Failure ]
 crbug.com/509025 [ Yosemite ] http/tests/misc/acid2.html [ Failure ]
 crbug.com/509025 [ Yosemite ] http/tests/navigation/navigation-redirect-schedule-crash.html [ Failure ]
 crbug.com/509025 [ Yosemite ] http/tests/security/contentTypeOptions/nosniff-script-without-content-type-blocked.html [ Failure ]
 crbug.com/509025 [ Yosemite ] media/video-paint-invalidation.html [ Failure ]
 crbug.com/509025 [ Yosemite ] paint/invalidation/animated-gif-background.html [ Failure ]
 crbug.com/509025 [ Yosemite ] paint/invalidation/animated-gif.html [ Failure ]
 crbug.com/509025 [ Yosemite ] svg/custom/absolute-sized-content-with-resources.xhtml [ Failure ]
 crbug.com/509025 [ Yosemite ] svg/custom/bug78807.svg [ Failure ]
 crbug.com/509025 [ Yosemite ] svg/text/text-rescale.html [ Failure ]
-crbug.com/509025 [ Yosemite ] virtual/prefer_compositing_to_lcd_text/compositing/overflow/textarea-scroll-touch.html [ Failure ]
 crbug.com/509025 [ Yosemite ] compositing/geometry/fixed-position-iframe-composited-page-scale-down.html [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] compositing/geometry/fixed-position-iframe-composited-page-scale.html [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] compositing/iframes/iframe-copy-on-scroll.html [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] compositing/overflow/do-not-paint-outline-into-composited-scrolling-contents.html [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] compositing/overflow/update-widget-positions-on-nested-frames-and-scrollers.html [ ImageOnlyFailure Failure Timeout ]
 crbug.com/509025 [ Yosemite ] compositing/plugins/composited-plugin.html [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] compositing/visibility/visibility-image-layers.html [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] css2.1/20110323/abspos-containing-block-initial-001.htm [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] css2.1/20110323/block-non-replaced-height-002.htm [ ImageOnlyFailure ]
 crbug.com/509025 [ Yosemite ] css2.1/20110323/block-non-replaced-height-004.htm [ ImageOnlyFailure ]
@@ skipping 830 matching lines @@
 crbug.com/516522 [ Yosemite ] editing/selection/vertical-rl-rtl-extend-line-forward-p.html [ Failure ]
 
 crbug.com/521124 [ XP Win7 ] fast/css/font-weight-1.html [ ImageOnlyFailure ]
 
 crbug.com/502927 [ XP ] paint/frames/frameset-with-stacking-context-and-not-stacking-context-children.html [ Failure ]
 crbug.com/502927 [ XP ] paint/frames/frameset-with-stacking-contexts.html [ Failure ]
 
 # Temporarily allow failure until chromium change is landed and the test
 # expectation is updated.
 crbug.com/523073 media/video-display-aspect-ratio.html [ Pass Failure ]