Initial draft - modify ViewportAnchor to know about both inner and outer viewports.

Source/web/ViewportAnchor.h

Index: Source/web/ViewportAnchor.h
diff --git a/Source/web/ViewportAnchor.h b/Source/web/ViewportAnchor.h
index 8bd0a7b92b1ef0c77917e4b37fc754c2e69e768d..d3331481e65a32557726237fc7d0909b3f55db5e 100644
--- a/Source/web/ViewportAnchor.h
+++ b/Source/web/ViewportAnchor.h
@@ -43,6 +43,7 @@ namespace blink {
 class EventHandler;
 class IntSize;
 class Node;
+class ScrollView;
 
 // ViewportAnchor provides a way to anchor a viewport origin to a DOM node.
 // In particular, the user supplies the current viewport (in CSS coordinates)
@@ -56,19 +57,28 @@ class ViewportAnchor {
 public:
     explicit ViewportAnchor(EventHandler*);
 
-    void setAnchor(const IntRect& viewRect, const FloatSize& anchorInViewCoords);
+    void setAnchor(const IntRect& outerViewRect, const IntRect& innerViewRect, const FloatSize& anchorInViewCoords);
 
-    IntPoint computeOrigin(const IntSize& currentViewSize) const;
+    void computeOrigins(const ScrollView& frameView, const FloatSize& innerSize,

[leviw_travelin_and_unemployed, 2014/09/18 18:49:54]

ScrollView& frameView? Really you should leave that identifier out of the
header.

[timav, 2014/09/19 17:38:43]

Done.

+        IntPoint* mainFrameOffset, FloatPoint* pinchViewportOffset) const;

[leviw_travelin_and_unemployed, 2014/09/18 18:49:54]

These appear to never be null. Why are you passing them as pointers instead of
references?

[timav, 2014/09/19 17:38:43]

I'm passing pointers because I think it would better indicate to a caller that
they are output parameters.
  f() { ... g(a, &b); ... }
versus
  f() { ... g(a, b); ... }
I think the first variant better describes my intention to modify 'b'.

Of course if there is a WebKit policy to always use references in such cases or
if you strongly prefer the second way I'll change the code.

+
+private:
+    FloatPoint getInnerOrigin(const FloatSize& innerSize) const;
 
 private:
     RawPtrWillBeMember<EventHandler> m_eventHandler;
 
-    IntRect m_viewRect;
+    // Inner viewport origin in the reference frame of the document in CSS pixels
+    FloatPoint m_pinchViewportInDocument;
+
+    // Inner viewport origin in the reference frame of the outer viewport
+    // normalized to the outer viewport size.
+    FloatSize m_normalizedPinchViewportOffset;
 
     RefPtrWillBeMember<Node> m_anchorNode;
     LayoutRect m_anchorNodeBounds;
 
-    FloatSize m_anchorInViewCoords;
+    FloatSize m_anchorInInnerViewCoords;
     FloatSize m_anchorInNodeCoords;
 };