Improve scroll anchoring's interactions with the visual viewport

third_party/WebKit/Source/core/frame/VisualViewport.cpp

Index: third_party/WebKit/Source/core/frame/VisualViewport.cpp
diff --git a/third_party/WebKit/Source/core/frame/VisualViewport.cpp b/third_party/WebKit/Source/core/frame/VisualViewport.cpp
index fe5ac4494ee2ecb6dc58e36d675b0f7f4d2dad20..da1e5a8e5a4ca0824f43d43df1ca8a8ab127f02f 100644
--- a/third_party/WebKit/Source/core/frame/VisualViewport.cpp
+++ b/third_party/WebKit/Source/core/frame/VisualViewport.cpp
@@ -273,8 +273,14 @@ double VisualViewport::pageScale()
 
 void VisualViewport::setScaleAndLocation(float scale, const FloatPoint& location)
 {
+    if (didSetScaleOrLocation(scale, location))
+        clearScrollAnchor();
+}
+
+bool VisualViewport::didSetScaleOrLocation(float scale, const FloatPoint& location)
+{
     if (!mainFrame())
-        return;
+        return false;
 
     bool valuesChanged = false;
 
@@ -307,12 +313,23 @@ void VisualViewport::setScaleAndLocation(float scale, const FloatPoint& location
     }
 
     if (!valuesChanged)
-        return;
+        return false;
 
     InspectorInstrumentation::didUpdateLayout(mainFrame());
     mainFrame()->loader().saveScrollState();
 
     clampToBoundaries();
+
+    return true;
+}
+
+void VisualViewport::clearScrollAnchor()
+{
+    if (RuntimeEnabledFeatures::scrollAnchoringEnabled()) {
+        LocalFrame* frame = mainFrame();
+        if (frame && frame->view())
+            frame->view()->clearScrollAnchor();
+    }
 }
 
 bool VisualViewport::magnifyScaleAroundAnchor(float magnifyDelta, const FloatPoint& anchor)
@@ -631,9 +648,10 @@ IntSize VisualViewport::contentsSize() const
     return frame->view()->visibleContentRect(IncludeScrollbars).size();
 }
 
-void VisualViewport::setScrollOffset(const DoublePoint& offset, ScrollType)
+void VisualViewport::setScrollOffset(const DoublePoint& offset, ScrollType scrollType)
 {
-    setLocation(toFloatPoint(offset));
+    if (didSetScaleOrLocation(m_scale, toFloatPoint(offset)) && scrollType != AnchoringScroll)
+        clearScrollAnchor();
 }
 
 GraphicsLayer* VisualViewport::layerForContainer() const