Adds scroll position/scale emulation to DevTools.

third_party/WebKit/Source/core/frame/FrameView.h

Index: third_party/WebKit/Source/core/frame/FrameView.h
diff --git a/third_party/WebKit/Source/core/frame/FrameView.h b/third_party/WebKit/Source/core/frame/FrameView.h
index d247ae99205dcf52081dcebd2b5c07510a1fd99f..a2298edf51031bb73c03d55c91997ada30ff75f0 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.h
+++ b/third_party/WebKit/Source/core/frame/FrameView.h
@@ -190,6 +190,11 @@ public:
 
     void setScrollPosition(const DoublePoint&, ScrollType, ScrollBehavior = ScrollBehaviorInstant) override;
 
+    // Override the scroll position with a fixed value.
+    void setScrollOverride(const DoublePoint& position);
+    // Clear the scroll position override.
+    void clearScrollOverride();
+
     void didUpdateElasticOverscroll();
 
     void viewportSizeChanged(bool widthChanged, bool heightChanged);
@@ -647,6 +652,7 @@ private:
     explicit FrameView(LocalFrame*);
 
     void setScrollOffset(const DoublePoint&, ScrollType) override;
+    DoublePoint applyScrollOverrideToPosition(const DoublePoint& position);
 
     enum LifeCycleUpdateOption {
         OnlyUpToLayoutClean,
@@ -870,6 +876,9 @@ private:
     DoublePoint m_scrollPosition;
     IntSize m_contentsSize;
 
+    bool m_scrollOverrideEnabled;
+    DoublePoint m_scrollOverridePosition;
+
     int m_scrollbarsAvoidingResizer;
     bool m_scrollbarsSuppressed;