Add some modifiers to eventSender for test.

content/shell/renderer/test_runner/event_sender.cc

Index: content/shell/renderer/test_runner/event_sender.cc
diff --git a/content/shell/renderer/test_runner/event_sender.cc b/content/shell/renderer/test_runner/event_sender.cc
index 4c90eb413004dc5e1644f4fbda21b9a952ef0053..3265d036385eb38416e5d2da73a9765bc79a976e 100644
--- a/content/shell/renderer/test_runner/event_sender.cc
+++ b/content/shell/renderer/test_runner/event_sender.cc
@@ -93,6 +93,12 @@ int GetKeyModifier(const std::string& modifier_name) {
 #else
     return WebInputEvent::ControlKey;
 #endif
+  } else if (!strcmp(characters, "leftButton")) {
+    return WebInputEvent::LeftButtonDown;
+  } else if (!strcmp(characters, "middleButton")) {
+    return WebInputEvent::MiddleButtonDown;
+  } else if (!strcmp(characters, "rightButton")) {
+    return WebInputEvent::RightButtonDown;
   }
 
   return 0;