[blink] Add a DocumentMarker::MisspellingMarkers helper

Source/core/dom/DocumentMarker.h

Index: Source/core/dom/DocumentMarker.h
diff --git a/Source/core/dom/DocumentMarker.h b/Source/core/dom/DocumentMarker.h
index b6072b9701c76607f4cd735443d80bbe8d2538b9..f4410fbdc3f30c0942f2cbed661f7736221a7f9e 100644
--- a/Source/core/dom/DocumentMarker.h
+++ b/Source/core/dom/DocumentMarker.h
@@ -68,6 +68,14 @@ public:
         }
     };
 
+    class MisspellingMarkers : public MarkerTypes {
+    public:
+        MisspellingMarkers()
+            : MarkerTypes(Spelling | Grammar)
+        {
+        }
+    };
+
     DocumentMarker();
     DocumentMarker(MarkerType, unsigned startOffset, unsigned endOffset);
     DocumentMarker(MarkerType, unsigned startOffset, unsigned endOffset, const String& description);