Adds DevTools commands for forced viewport override.

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 7cf81e9a6ff81b8a5ea70ba08710466ae6e12505..311b92ac2ebbccdce9f7ec0ac9a9c32ab5be6fe6 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.h
+++ b/third_party/WebKit/Source/core/frame/FrameView.h
@@ -190,6 +190,7 @@ public:
     void setInputEventsTransformForEmulation(const IntSize&, float);
 
     void setScrollPosition(const DoublePoint&, ScrollType, ScrollBehavior = ScrollBehaviorInstant) override;
+    void didChangeScrollOffset();
 
     void didUpdateElasticOverscroll();
 
@@ -448,6 +449,13 @@ public:
     IntRect visibleContentRect(IncludeScrollbarsInRect = ExcludeScrollbars) const override;
     IntSize visibleContentSize(IncludeScrollbarsInRect = ExcludeScrollbars) const;
 
+    // Set a custom painting area. Used for visual transform overrides to ensure
+    // that the content inside the overridden visible area is painted. If not
+    // set, the painting area defaults to visibleContentRect().
+    void setVisibleContentRectForPainting(const IntRect&);
+    void resetVisibleContentRectForPainting();
+    IntRect visibleContentRectForPainting() const;
+
     // Functions for getting/setting the size of the document contained inside the FrameView (as an IntSize or as individual width and height
     // values).
     IntSize contentsSize() const override; // Always at least as big as the visibleWidth()/visibleHeight().
@@ -874,6 +882,7 @@ private:
     DoubleSize m_pendingScrollDelta;
     DoublePoint m_scrollPosition;
     IntSize m_contentsSize;
+    std::unique_ptr<IntRect> m_visibleContentRectForPainting;

[Sami, 2016/08/11 13:24:24]

Could this be a WTF::Optional?

[Eric Seckler, 2016/08/11 15:12:38]

Indeed :)

 
     int m_scrollbarsAvoidingResizer;
     bool m_scrollbarsSuppressed;