[root layer scrolls] Fix subpixel-shadow-included-in-invalidation.html

This test depends on invalidations on a specific layer. With root layer
scrolls enabled, the paint invalidations for this test are on the
scrolling contents layer which is not the first layer.

Bug: 781419

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_root_layer_scrolls
Change-Id: I86d50174eb74c2481849752e4e506384d489c9b6
Reviewed-on: https://chromium-review.googlesource.com/764383Reviewed-by: Steve Kobes <skobes@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515812}

third_party/WebKit/LayoutTests/FlagExpectations/root-layer-scrolls

@@ -96,7 +96,6 @@ crbug.com/417782 paint/invalidation/media-audio-no-spurious-repaints.html [ Fail
 crbug.com/417782 paint/invalidation/overflow-scroll-body-appear.html [ Failure ]
 crbug.com/417782 paint/invalidation/positioned-document-element.html [ Crash ]
 crbug.com/417782 paint/invalidation/resize-iframe-text.html [ Failure ]
-crbug.com/417782 paint/invalidation/subpixel-shadow-included-in-invalidation.html [ Failure ]
 crbug.com/417782 paint/invalidation/svg/absolute-sized-document-no-scrollbars.svg [ Failure ]
 crbug.com/417782 paint/invalidation/svg/deep-nested-embedded-svg-size-changes-no-layout-triggers-1.html [ Failure ]
 crbug.com/417782 paint/invalidation/svg/deep-nested-embedded-svg-size-changes-no-layout-triggers-2.html [ Failure ]

third_party/WebKit/LayoutTests/paint/invalidation/subpixel-shadow-included-in-invalidation.html

@@ -41,7 +41,8 @@ runAfterLayoutAndPaint(function() {
                 return;
             var layers_dump = internals.layerTreeAsText(document, internals.LAYER_TREE_INCLUDES_PAINT_INVALIDATIONS);
             var layers = JSON.parse(layers_dump).layers;
-            var paintInvalidations = layers[0].paintInvalidations;
+            var scrollingContentsLayer = internals.runtimeFlags.rootLayerScrollingEnabled ? layers[2] : layers[0];
+            var paintInvalidations = scrollingContentsLayer.paintInvalidations;
             var shadowRect = [1.4, 1.4, 100, 100];
             assert_true(paintInvalidations.some(paintInvalidation => rectContainsRect(paintInvalidation.rect, shadowRect)),
                         'Subpixel shadow ' + JSON.stringify(shadowRect) + ' should be repainted. ' + layers_dump);