Make rootScroller the layout viewport.

third_party/WebKit/Source/core/frame/RootFrameViewportTest.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 "core/frame/RootFrameViewport.h"
 
 #include "core/layout/ScrollAlignment.h"
 #include "platform/geometry/DoubleRect.h"
 #include "platform/geometry/LayoutRect.h"
 #include "platform/scroll/ScrollableArea.h"
@@ skipping 423 matching lines @@
 
     rootFrameViewport->setScrollPosition(DoublePoint(40, 40), UserScroll);
     EXPECT_POINT_EQ(DoublePoint(40, 40), visualViewport->scrollPositionDouble());
     EXPECT_POINT_EQ(DoublePoint(0, 0), layoutViewport->scrollPositionDouble());
 
     rootFrameViewport->setScrollPosition(DoublePoint(60, 60), ProgrammaticScroll);
     EXPECT_POINT_EQ(DoublePoint(50, 50), visualViewport->scrollPositionDouble());
     EXPECT_POINT_EQ(DoublePoint(10, 10), layoutViewport->scrollPositionDouble());
 }
 
+// Tests that setting an alternate layout viewport scrolls the alternate
+// instead of the original.
+TEST_F(RootFrameViewportTest, SetAlternateLayoutViewport)
+{
+    IntSize viewportSize(100, 100);
+    RootFrameViewStub* layoutViewport = RootFrameViewStub::create(viewportSize, IntSize(200, 300));
+    VisualViewportStub* visualViewport = VisualViewportStub::create(viewportSize, viewportSize);
+
+    RootFrameViewStub* alternateScroller = RootFrameViewStub::create(viewportSize, IntSize(600, 500));
+
+    RootFrameViewport* rootFrameViewport =
+        RootFrameViewport::create(*visualViewport, *layoutViewport);
+
+    visualViewport->setScale(2);
+
+    rootFrameViewport->setScrollPosition(DoublePoint(100, 100), UserScroll);
+    EXPECT_POINT_EQ(DoublePoint(50, 50), visualViewport->scrollPositionDouble());
+    EXPECT_POINT_EQ(DoublePoint(50, 50), layoutViewport->scrollPositionDouble());
+    EXPECT_POINT_EQ(DoublePoint(100, 100), rootFrameViewport->scrollPositionDouble());
+
+    rootFrameViewport->setLayoutViewport(*alternateScroller);
+    EXPECT_POINT_EQ(DoublePoint(50, 50), visualViewport->scrollPositionDouble());
+    EXPECT_POINT_EQ(DoublePoint(0, 0), alternateScroller->scrollPositionDouble());
+    EXPECT_POINT_EQ(DoublePoint(50, 50), rootFrameViewport->scrollPositionDouble());
+
+    rootFrameViewport->setScrollPosition(DoublePoint(200, 200), UserScroll);
+    EXPECT_POINT_EQ(DoublePoint(50, 50), visualViewport->scrollPositionDouble());
+    EXPECT_POINT_EQ(DoublePoint(150, 150), alternateScroller->scrollPositionDouble());
+    EXPECT_POINT_EQ(DoublePoint(200, 200), rootFrameViewport->scrollPositionDouble());
+    EXPECT_POINT_EQ(DoublePoint(50, 50), layoutViewport->scrollPositionDouble());
+
+    EXPECT_POINT_EQ(DoublePoint(550, 450), rootFrameViewport->maximumScrollPositionDouble());
+}
+
 } // namespace blink