Remove DocumentParser::flush which is not used by anyone.

third_party/WebKit/Source/core/dom/RawDataDocumentParser.h

Index: third_party/WebKit/Source/core/dom/RawDataDocumentParser.h
diff --git a/third_party/WebKit/Source/core/dom/RawDataDocumentParser.h b/third_party/WebKit/Source/core/dom/RawDataDocumentParser.h
index 6f7c7edf1119ab023b028516bd9b0092513fa11f..9435f7f11e273ebf62f67fef1ae06058f3aace24 100644
--- a/third_party/WebKit/Source/core/dom/RawDataDocumentParser.h
+++ b/third_party/WebKit/Source/core/dom/RawDataDocumentParser.h
@@ -45,17 +45,9 @@ protected:
     }
 
 private:
-    void flush() override
-    {
-        // Make sure appendBytes is called at least once.
-        appendBytes(0, 0);
-    }
-
-    void insert(const SegmentedString&) override
-    {
-    }
+    void insert(const SegmentedString&) final {}
 
-    void append(const String&) override
+    void append(const String&) final
     {
         ASSERT_NOT_REACHED();
     }