Fix main thread top controls scrolling to mirror CC.

third_party/WebKit/Source/web/WebViewImpl.cpp

Index: third_party/WebKit/Source/web/WebViewImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebViewImpl.cpp b/third_party/WebKit/Source/web/WebViewImpl.cpp
index 98b04285fcb22d795e62fbf56591a796e7734f21..f66f9eb18954d85f3c84b9e73b8d954c8dfbf2d7 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -1827,11 +1827,30 @@ void WebViewImpl::didUpdateTopControls()
         return;
 
     VisualViewport& visualViewport = page()->frameHost().visualViewport();
-    float topControlsViewportAdjustment = topControls().layoutHeight() - topControls().contentOffset();
-    visualViewport.setTopControlsAdjustment(topControlsViewportAdjustment);
 
-    // Shrink the FrameView by the amount that will maintain the aspect-ratio with the VisualViewport.
-    view->setTopControlsViewportAdjustment(topControlsViewportAdjustment / minimumPageScaleFactor());
+    {
+        // This object will save the current visual viewport offset w.r.t. the
+        // document and restore it when the object goes out of scope. It's
+        // needed since the top controls adjustment will change the maximum
+        // scroll offset and we may need to reposition them to keep the user's
+        // apparent position unchanged.
+        ResizeViewportAnchor anchor(*view, visualViewport);
+
+        float topControlsViewportAdjustment =
+            topControls().layoutHeight() - topControls().contentOffset();
+        visualViewport.setTopControlsAdjustment(topControlsViewportAdjustment);
+
+        // Since the FrameView is sized to be the visual viewport at minimum
+        // scale, its adjustment must also be scaled by the minimum scale.
+        view->setTopControlsViewportAdjustment(
+            topControlsViewportAdjustment / minimumPageScaleFactor());
+
+        // Clamp the scroll offset of each viewport now that their bounds have
+        // changed. We'll try to restore hte saved scroll offset when anchor

[majidvp, 2016/04/01 17:09:36]

s/hte/the/

[bokan, 2016/04/05 17:11:40]

Done.

+        // goes out of scope.
+        visualViewport.clampToBoundaries();
+        view->setScrollPosition(view->scrollPositionDouble(), ProgrammaticScroll);

[majidvp, 2016/04/01 17:09:36]

Shouldn't this be unnecessary? The anchor sets the scroll position which should
also
clamp if necessary.

[bokan, 2016/04/05 17:11:40]

But the anchor needs the viewports to be at their clamped locations in order to
calculate where to restore them to (it works based on deltas in order to prevent
scrolling the layout viewport if it's unneeded). Admittedly this is more
appropriate in the anchoring code so I moved it there.

+    }
 }
 
 TopControls& WebViewImpl::topControls()
@@ -4330,25 +4349,32 @@ void WebViewImpl::applyViewportDeltas(
     if (!frameView)
         return;
 
+    ScrollableArea* layoutViewport = frameView->layoutViewportScrollableArea();
+    VisualViewport& visualViewport = page()->frameHost().visualViewport();
+
+    // Store the desired offsets for visual and layout viewports before setting
+    // the top controls ratio since doing so will change the bounds and move the
+    // viewports to keep the offsets valid. The compositor may have already done
+    // that so we don't want to double apply the deltas here.
+    FloatPoint visualViewportOffset = visualViewport.visibleRect().location();
+    visualViewportOffset.move(
+        visualViewportDelta.width,
+        visualViewportDelta.height);
+    DoublePoint layoutViewportPosition = layoutViewport->scrollPositionDouble()
+        + DoubleSize(layoutViewportDelta.width, layoutViewportDelta.height);
+
     topControls().setShownRatio(topControls().shownRatio() + topControlsShownRatioDelta);
 
-    FloatPoint visualViewportOffset = page()->frameHost().visualViewport().visibleRect().location();
-    visualViewportOffset.move(visualViewportDelta.width, visualViewportDelta.height);
     setPageScaleFactorAndLocation(pageScaleFactor() * pageScaleDelta, visualViewportOffset);
 
     if (pageScaleDelta != 1) {
         m_doubleTapZoomPending = false;
-        page()->frameHost().visualViewport().userDidChangeScale();
+        visualViewport.userDidChangeScale();
     }
 
     m_elasticOverscroll += elasticOverscrollDelta;
     frameView->didUpdateElasticOverscroll();
 
-    ScrollableArea* layoutViewport = frameView->layoutViewportScrollableArea();
-
-    DoublePoint layoutViewportPosition = layoutViewport->scrollPositionDouble()
-        + DoubleSize(layoutViewportDelta.width, layoutViewportDelta.height);
-
     if (layoutViewport->scrollPositionDouble() != layoutViewportPosition) {
         layoutViewport->setScrollPosition(layoutViewportPosition, CompositorScroll);
         if (DocumentLoader* documentLoader = mainFrameImpl()->frame()->loader().documentLoader())