Compute snap offsets (both repeat and element based)

Source/core/dom/ContainerNode.cpp

Index: Source/core/dom/ContainerNode.cpp
diff --git a/Source/core/dom/ContainerNode.cpp b/Source/core/dom/ContainerNode.cpp
index 5a44e55d67cbe96d456b2c3e4279929563e6b35a..066e5875a29671607113dc1bbf9dcaac9607d4c1 100644
--- a/Source/core/dom/ContainerNode.cpp
+++ b/Source/core/dom/ContainerNode.cpp
@@ -51,6 +51,7 @@
 #include "core/layout/LayoutTheme.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/line/InlineTextBox.h"
+#include "core/page/scrolling/SnapCoordinator.h"
 #include "platform/EventDispatchForbiddenScope.h"
 #include "platform/ScriptForbiddenScope.h"
 
@@ -872,12 +873,18 @@ void ContainerNode::attach(const AttachContext& context)
     attachChildren(context);
     clearChildNeedsStyleRecalc();
     Node::attach(context);
+
+    if (document().frame() && document().frame()->snapCoordinator())

[esprehn, 2015/09/24 17:37:41]

ditto checking for frame() doesn't make sense, this is also not the right layer
for this. This should be in Element, not ContainerNode.

[majidvp, 2015/10/15 21:47:02]

Done.

+        document().frame()->snapCoordinator()->attach(*this);
 }
 
 void ContainerNode::detach(const AttachContext& context)
 {
     detachChildren(context);
     setChildNeedsStyleRecalc();
+    if (document().frame() && document().frame()->snapCoordinator())
+        document().frame()->snapCoordinator()->detach(*this);

[esprehn, 2015/09/24 17:37:41]

frame() checks here don't make sense, we must have a frame if we're inside
detach. I also don't like the generic "detach" callbacks out to code like this.
This code should read like:

if (isSnapContainer())
  document().frameView()->removeSnapContainer(*this);
if (isSnapElement())
  document().frameView()->removeSnapElement(*this);

this code should also be in Element, not ContainerNode.

[majidvp, 2015/10/15 21:47:02]

Done.

+
     Node::detach(context);
 }