[SPV2] Implement the blink-side scroll property tree

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 55f071cafc334489d06d45c50113a5303dd18096..b171e8514602ba36e9bc30566a937eb7977a5813 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.h
+++ b/third_party/WebKit/Source/core/frame/FrameView.h
@@ -42,6 +42,7 @@
 #include "platform/graphics/Color.h"
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
+#include "platform/graphics/paint/ScrollPaintPropertyNode.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "platform/scroll/Scrollbar.h"
@@ -602,6 +603,9 @@ public:
     void setScrollTranslation(PassRefPtr<TransformPaintPropertyNode> scrollTranslation) { m_scrollTranslation = scrollTranslation; }
     TransformPaintPropertyNode* scrollTranslation() const { return m_scrollTranslation.get(); }
 
+    void setScroll(PassRefPtr<ScrollPaintPropertyNode> scroll) { m_scroll = scroll; }
+    ScrollPaintPropertyNode* scroll() const { return m_scroll.get(); }
+
     void setContentClip(PassRefPtr<ClipPaintPropertyNode> contentClip) { m_contentClip = contentClip; }
     ClipPaintPropertyNode* contentClip() const { return m_contentClip.get(); }
 
@@ -614,6 +618,9 @@ public:
     void setRootEffect(PassRefPtr<EffectPaintPropertyNode> rootEffect) { m_rootEffect = rootEffect; }
     EffectPaintPropertyNode* rootEffect() const { return m_rootEffect.get(); }
 
+    void setRootScroll(PassRefPtr<ScrollPaintPropertyNode> rootScroll) { m_rootScroll = rootScroll; }

[chrishtr, 2016/09/08 20:43:59]

Comments explaining the difference between scroll and root scroll?

[pdr., 2016/09/08 23:16:26]

The root nodes on FrameView just store no-op paint properties to match cc's
trees and to avoid using null for the root. This looks pretty silly for the
scroll tree.

I'd like to revisit the non-null root property tree node discussion...

Because we already differ from cc's trees at the root nodes (e.g., no viewport
transform yet), I think we should actually remove the no-op root nodes after all
and use null for the root of all trees. This would avoid needing to add a
scrollable=false bit just for the root scroll node. I could do this as a patch
before this patch. WDYT?

The primary downside to removing no-op root nodes is having to tell szager he
was right.

[chrishtr, 2016/09/09 16:27:28]

If you want to do that, I'd suggest after this patch rather than before. Forward
progess.

[trchen, 2016/09/09 22:03:17]

+1 The decision needs to be revisited.

IMO the decision to add no-op root nodes at blink property tree builder was not
very well thought (and I contributed part of the mess. Sorry.).

In my mind model the nullptr blink property node should just mean "whatever the
inherited context was". For example, for a top level compositor, nullptr
transform node means the window space, while for a OoP-frame it refers to the
transform space of the embedding foreign display item.

Also from the perspective of cc, property nodes #0 basically don't carry any
operation themselves, but just provide the context to be used for drawing or
getting inherited by child nodes. For example:
this.screen_space_transform = this.local_transform *
parent.screen_space_transform
In this case "local_transform" is an operation to modify
"screen_space_transform". And transform node #0's screen_space_transform is
hard-coded to be the device scale factor.

I think a cleaner model is that nullptr should just map to cc property node #0.
There are some cases that property node #1 has hard-coded operations. IMO we
should eliminate those special cases in cc. In the meantime we can generate
dummy nodes in PAC, and let nullptr maps to the dummy node.
+1 we can do it after.

+    ScrollPaintPropertyNode* rootScroll() const { return m_rootScroll.get(); }
+
     // TODO(ojan): Merge this with IntersectionObserver once it lands.
     IntRect computeVisibleArea();
 
@@ -920,6 +927,7 @@ private:
     // TODO(trchen): These will not be needed once settings->rootLayerScrolls() is enabled.
     RefPtr<TransformPaintPropertyNode> m_preTranslation;
     RefPtr<TransformPaintPropertyNode> m_scrollTranslation;
+    RefPtr<ScrollPaintPropertyNode> m_scroll;
     // The content clip clips the document (= LayoutView) but not the scrollbars.
     // TODO(trchen): This will not be needed once settings->rootLayerScrolls() is enabled.
     RefPtr<ClipPaintPropertyNode> m_contentClip;
@@ -929,6 +937,7 @@ private:
     RefPtr<TransformPaintPropertyNode> m_rootTransform;
     RefPtr<ClipPaintPropertyNode> m_rootClip;
     RefPtr<EffectPaintPropertyNode> m_rootEffect;
+    RefPtr<ScrollPaintPropertyNode> m_rootScroll;
 
     // This is set on the local root frame view only.
     DocumentLifecycle::LifecycleState m_currentUpdateLifecyclePhasesTargetState;