Add new API for only moving the selection extent point.

public/web/WebLocalFrame.h

Index: public/web/WebLocalFrame.h
diff --git a/public/web/WebLocalFrame.h b/public/web/WebLocalFrame.h
index e92eddc1dba82affa84e7e5aa2af4d7413728d91..99c324c5c1bf190eedb0447a3da546dabf904e66 100644
--- a/public/web/WebLocalFrame.h
+++ b/public/web/WebLocalFrame.h
@@ -67,6 +67,12 @@ public:
     // Associates an isolated world with human-readable name which is useful for
     // extension debugging.
     virtual void setIsolatedWorldHumanReadableName(int worldID, const WebString&) = 0;
+
+
+    // Selection --------------------------------------------------------------
+
+    // Move the selection extent point.
+    virtual void moveRangeSelectionExtent(const WebPoint&) = 0;
 };
 
 } // namespace blink