Recompute slow scroll regions after overflow recalc

LayoutTests/scrollingcoordinator/non-fast-scrollable-animation-expected.txt

Index: LayoutTests/scrollingcoordinator/non-fast-scrollable-animation-expected.txt
diff --git a/LayoutTests/scrollingcoordinator/non-fast-scrollable-animation-expected.txt b/LayoutTests/scrollingcoordinator/non-fast-scrollable-animation-expected.txt
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+++ b/LayoutTests/scrollingcoordinator/non-fast-scrollable-animation-expected.txt
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+
+A single square should be visible covered by a green overlay.
+
+This test ensures that animating a non-fast scrollable area correctly updates list of non-fast scrollable rects (See http://crbug.com/417345).
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS nonFastScrollableRects.length is 1
+PASS rectToString(nonFastScrollableRects[0]) is "[0, 0, 222, 222]"
+PASS internals.needsLayoutCount() is 0
+PASS internals.needsLayoutCount() is 0
+PASS internals.needsLayoutCount() is 0
+PASS nonFastScrollableRects.length is 1
+PASS rectToString(nonFastScrollableRects[0]) is "[100, 100, 222, 222]"
+PASS successfullyParsed is true
+
+TEST COMPLETE
+