Adds scroll position/scale emulation to DevTools.

third_party/WebKit/Source/web/WebViewImpl.h

Index: third_party/WebKit/Source/web/WebViewImpl.h
diff --git a/third_party/WebKit/Source/web/WebViewImpl.h b/third_party/WebKit/Source/web/WebViewImpl.h
index 1b130a7368a06b6ecaefac789f3004d5baecac32..9d473fbd4404952980d565594637eb9a05835297 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.h
+++ b/third_party/WebKit/Source/web/WebViewImpl.h
@@ -49,6 +49,7 @@
 #include "public/platform/WebSize.h"
 #include "public/platform/WebString.h"
 #include "public/platform/WebVector.h"
+#include "public/web/WebDeviceEmulationParams.h"
 #include "public/web/WebInputEvent.h"
 #include "public/web/WebNavigationPolicy.h"
 #include "public/web/WebPageImportanceSignals.h"
@@ -205,6 +206,7 @@ public:
     void setInitialPageScaleOverride(float) override;
     void setMaximumLegibleScale(float) override;
     void setPageScaleFactor(float) override;
+    WebPoint mainFrameOffset() const override;
     void setVisualViewportOffset(const WebFloatPoint&) override;
     WebFloatPoint visualViewportOffset() const override;
     WebFloatSize visualViewportSize() const override;
@@ -538,6 +540,12 @@ private:
     void setPageScaleFactorAndLocation(float, const FloatPoint&);
     void propagateZoomFactorToLocalFrameRoots(Frame*, float);
 
+    // Override the page scale and scroll positions of main frame and visual viewport.
+    void setScrollOverride(const WebDeviceEmulationParams&);
+
+    // Clear the page scale and scroll position overrides.
+    void clearScrollOverride();
+
     void scrollAndRescaleViewports(float scaleFactor, const IntPoint& mainFrameOrigin, const FloatPoint& visualViewportOrigin);
 
     float maximumLegiblePageScale() const;
@@ -678,6 +686,9 @@ private:
     float m_fakePageScaleAnimationPageScaleFactor;
     bool m_fakePageScaleAnimationUseAnchor;
 
+    bool m_scrollOverrideEnabled;
+    WebDeviceEmulationParams m_scrollOverrideParams;

[Sami, 2016/06/23 17:34:03]

This is a pretty hefty object -- should we instead just store the couple of
fields we need here?

[Eric Seckler, 2016/06/23 18:12:43]

I agree, I will do that in combination with David's suggestion to extract the
data and some of the logic for applying overrides (e.g.
VisualViewport::applyScrollOverrideToLocation()) into a separate class.

I was experimenting with making the VisualViewport::setSize() call in
WebViewImpl::performResize() dependent on whether a visual viewport size
override is set (see WebViewImpl.cpp in patch) to avoid crbug.com/620772 for our
use cases. I'll remove that in the process as it is a little ugly - There's no
other reason why WebViewImpl (or the new class for scroll overrides) should know
about viewport sizes. Does that make sense?

+
     bool m_doingDragAndDrop;
 
     bool m_ignoreInputEvents;