Add DocumentMarkerList in preparation for DocumentMarkerController refactor

third_party/WebKit/Source/core/editing/BUILD.gn

Index: third_party/WebKit/Source/core/editing/BUILD.gn
diff --git a/third_party/WebKit/Source/core/editing/BUILD.gn b/third_party/WebKit/Source/core/editing/BUILD.gn
index 3215672513de53dc7000c50ba4e276ef01f4656d..583c3553d167d2954598ee255031e32b46c707b3 100644
--- a/third_party/WebKit/Source/core/editing/BUILD.gn
+++ b/third_party/WebKit/Source/core/editing/BUILD.gn
@@ -190,6 +190,8 @@ blink_core_sources("editing") {
     "markers/DocumentMarker.h",
     "markers/DocumentMarkerController.cpp",
     "markers/DocumentMarkerController.h",
+    "markers/DocumentMarkerList.cpp",
+    "markers/DocumentMarkerList.h",
     "markers/RenderedDocumentMarker.h",
     "serializers/HTMLInterchange.cpp",
     "serializers/HTMLInterchange.h",
@@ -284,6 +286,7 @@ source_set("unit_tests") {
     "iterators/TextIteratorTest.cpp",
     "iterators/TextSearcherICUTest.cpp",
     "markers/DocumentMarkerControllerTest.cpp",
+    "markers/DocumentMarkerListTest.cpp",
     "markers/DocumentMarkerTest.cpp",
     "serializers/StyledMarkupSerializerTest.cpp",
     "spellcheck/IdleSpellCheckCallbackTest.cpp",