Enable slimming paint by default (for trybots only)

Source/core/paint/DisplayItemListPaintTest.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "platform/graphics/paint/DisplayItemList.h"
 
 #include "core/layout/LayoutTestHelper.h"
 #include "core/layout/LayoutText.h"
 #include "core/layout/LayoutView.h"
@@ skipping 29 matching lines @@
 
         RenderingTest::SetUp();
         enableCompositing();
 
         m_layoutView = document().view()->layoutView();
         ASSERT_TRUE(m_layoutView);
     }
 
     virtual void TearDown() override
     {
-        RuntimeEnabledFeatures::setSlimmingPaintEnabled(false);
+        // RuntimeEnabledFeatures::setSlimmingPaintEnabled(false);
     }
 
     LayoutView* m_layoutView;
 };
 
 class TestDisplayItem : public DisplayItem {
 public:
     TestDisplayItem(const DisplayItemClientWrapper& client, Type type) : DisplayItem(client, type) { }
 
     virtual void replay(GraphicsContext&) override final { ASSERT_NOT_REACHED(); }
@@ skipping 89 matching lines @@
     InlineTextBox& newFirstTextBox = *newText.firstTextBox();
     InlineTextBox& secondTextBox = *newText.firstTextBox()->nextTextBox();
 
     EXPECT_DISPLAY_LIST(rootDisplayItemList().displayItems(), 3,
         TestDisplayItem(htmlObject, DisplayItem::BoxDecorationBackground),
         TestDisplayItem(newFirstTextBox, DisplayItem::paintPhaseToDrawingType(PaintPhaseForeground)),
         TestDisplayItem(secondTextBox, DisplayItem::paintPhaseToDrawingType(PaintPhaseForeground)));
 }
 
 } // namespace blink