[root layer scrolls] Rebaseline passing fixed-background-scroll-window

This patch adds platform-specific expectations to this passing test.

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_root_layer_scrolls
Change-Id: I985ce12ac1aafa21eaefa7836422e051df3e07f4
Reviewed-on: https://chromium-review.googlesource.com/803659
Commit-Queue: Philip Rogers <pdr@chromium.org>
Commit-Queue: Stefan Zager <szager@chromium.org>
Reviewed-by: Stefan Zager <szager@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521037}

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

@@ -48,7 +48,6 @@ crbug.com/417782 inspector-protocol/dom-snapshot/dom-snapshot-getSnapshot.js [ F
 crbug.com/417782 inspector-protocol/layers/paint-profiler.js [ Crash ]
 crbug.com/417782 inspector-protocol/page/get-layout-metrics.js [ Failure ]
 crbug.com/417782 paint/invalidation/window-resize/window-resize-vertical-writing-mode.html [ Crash ]
-crbug.com/417782 [ Mac Win ] paint/overflow/fixed-background-scroll-window.html [ Failure ]
 crbug.com/417782 plugins/webview-plugin-nested-iframe-scroll.html [ Failure ]
 crbug.com/417782 plugins/webview-plugin-scroll.html [ Failure ]
 crbug.com/417782 transforms/selection-bounds-in-transformed-view.html [ Failure ]

third_party/WebKit/LayoutTests/flag-specific/root-layer-scrolls/platform/mac/paint/overflow/fixed-background-scroll-window-expected.txt

+layer at (0,0) size 800x600 scrollY 1000.00 scrollHeight 4016
+  LayoutView at (0,0) size 800x600
+layer at (0,-1000) size 800x4016 backgroundClip at (0,0) size 800x600 clip at (0,0) size 800x600
+  LayoutBlockFlow {HTML} at (0,0) size 800x4016
+    LayoutBlockFlow {BODY} at (8,8) size 784x4000
+layer at (8,116) size 666x18
+  LayoutBlockFlow (positioned) {P} at (8,1116) size 665.63x18
+    LayoutText {#text} at (0,0) size 666x18
+      text run at (0,0) width 666: "Tests painting of fixed background content in scrolled container. Passes if the background doesn't scroll."
+scrolled to 0,1000
\ No newline at end of file

third_party/WebKit/LayoutTests/flag-specific/root-layer-scrolls/platform/win/paint/overflow/fixed-background-scroll-window-expected.txt

+layer at (0,0) size 800x600 scrollY 1000.00 scrollHeight 4016
+  LayoutView at (0,0) size 800x600
+layer at (0,-1000) size 800x4016 backgroundClip at (0,0) size 800x600 clip at (0,0) size 800x600
+  LayoutBlockFlow {HTML} at (0,0) size 800x4016
+    LayoutBlockFlow {BODY} at (8,8) size 784x4000
+layer at (8,116) size 622x20
+  LayoutBlockFlow (positioned) {P} at (8,1116) size 622x20
+    LayoutText {#text} at (0,0) size 622x19
+      text run at (0,0) width 622: "Tests painting of fixed background content in scrolled container. Passes if the background doesn't scroll."
+scrolled to 0,1000
\ No newline at end of file