Compute snap offsets (both repeat and element based)

third_party/WebKit/Source/core/dom/Document.cpp

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index 310aa4148998d4807b89e1941c69b1336f076be8..a1726a717250851b291bdd544bcca3b6f006862f 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -189,6 +189,7 @@
 #include "core/page/Page.h"
 #include "core/page/PointerLockController.h"
 #include "core/page/scrolling/ScrollingCoordinator.h"
+#include "core/page/scrolling/SnapCoordinator.h"
 #include "core/svg/SVGDocumentExtensions.h"
 #include "core/svg/SVGTitleElement.h"
 #include "core/svg/SVGUseElement.h"
@@ -5329,6 +5330,14 @@ bool Document::threadedParsingEnabledForTesting()
     return s_threadedParsingEnabledForTesting;
 }
 
+SnapCoordinator* Document::snapCoordinator()
+{
+    if (RuntimeEnabledFeatures::cssScrollSnapPointsEnabled() && !m_snapCoordinator)
+        m_snapCoordinator = SnapCoordinator::create();
+
+    return m_snapCoordinator.get();
+}
+
 bool Document::hasActiveParser()
 {
     return m_activeParserCount || (m_parser && m_parser->processingData());
@@ -5831,6 +5840,7 @@ DEFINE_TRACE(Document)
     visitor->trace(m_compositorPendingAnimations);
     visitor->trace(m_contextDocument);
     visitor->trace(m_canvasFontCache);
+    visitor->trace(m_snapCoordinator);
     WillBeHeapSupplementable<Document>::trace(visitor);
 #endif
     TreeScope::trace(visitor);