[Squad] Clone ComputedStyle before changing for overscroll test.

To prepare for immutable ComputedStyle objects.

Bug: 813068
Change-Id: Id5b4a57940712adfc9d353634856bc32e4ef2a0d
Reviewed-on: https://chromium-review.googlesource.com/979810Reviewed-by: Stefan Zager <szager@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545867}

third_party/WebKit/Source/core/input/OverscrollBehaviorTest.cpp

@@ -61,8 +61,11 @@ void OverscrollBehaviorTest::SetUp() {
 void OverscrollBehaviorTest::SetInnerOverscrollBehavior(EOverscrollBehavior x,
                                                         EOverscrollBehavior y) {
   Element* inner = GetDocument().getElementById("inner");
-  inner->MutableComputedStyle()->SetOverscrollBehaviorX(x);
-  inner->MutableComputedStyle()->SetOverscrollBehaviorY(y);
+  scoped_refptr<ComputedStyle> modified_style =
+      ComputedStyle::Clone(*inner->GetComputedStyle());
+  modified_style->SetOverscrollBehaviorX(x);
+  modified_style->SetOverscrollBehaviorY(y);
+  inner->GetLayoutObject()->SetStyle(std::move(modified_style));
 }
 
 void OverscrollBehaviorTest::ScrollBegin(double hint_x, double hint_y) {