EventSender: Added checks for missing arguments

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 392ef75ea5a6f8cd9efe833e410109f504a27653..7d49dcee8aac3864046052ab7aa962f60160908d 100644
--- a/content/shell/renderer/test_runner/event_sender.cc
+++ b/content/shell/renderer/test_runner/event_sender.cc
@@ -1922,11 +1922,10 @@ void EventSender::SendCurrentTouchEvent(WebInputEvent::Type type) {
 
 void EventSender::GestureEvent(WebInputEvent::Type type,
                                gin::Arguments* args) {
-  double x;
-  double y;
-  args->GetNext(&x);
-  args->GetNext(&y);
-  WebPoint point(x, y);
+  double x = 0;
+  double y = 0;
+  DCHECK(args->GetNext(&x));

[Rick Byers, 2014/09/23 14:27:14]

I think we should check to see if there are args and fail gracefully (with an
exception) if there isn't.  See the uses of args->PeekNext().IsEmpty()
throughout this file.  The main reason to do this even though this is only test
code is that we do fuzz testing that creates semi-random html/JavaScript pages
that may make use of EventSender (eg. see http://crbug.com/390623).  So any
crash you can trigger with EventSender is a potential clusterfuzz failure point
(which would ultimately be a false positive since it doesn't ship, but still
worth avoiding the noise).

[earthdok, 2014/09/23 14:33:08]

DCHECKs aren't evaluated in Release builds, so this function call won't happen.
Worse, MSan can no longer catch this bug because you've pre-initialized the
variables (though in this particular case you'll get a compiler warning about
unused variables).

Why not change those to CHECKs, and remove explicit zero-initialization of x and
y?

+  DCHECK(args->GetNext(&y));
 
   WebGestureEvent event;
   event.type = type;
@@ -1944,7 +1943,7 @@ void EventSender::GestureEvent(WebInputEvent::Type type,
           current_gesture_location_.y + event.data.scrollUpdate.deltaY;
       break;
     case WebInputEvent::GestureScrollBegin:
-      current_gesture_location_ = WebPoint(point.x, point.y);
+      current_gesture_location_ = WebPoint(x, y);
       event.x = current_gesture_location_.x;
       event.y = current_gesture_location_.y;
       break;
@@ -1979,8 +1978,8 @@ void EventSender::GestureEvent(WebInputEvent::Type type,
       event.data.tap.tapCount = tap_count;
       event.data.tap.width = width;
       event.data.tap.height = height;
-      event.x = point.x;
-      event.y = point.y;
+      event.x = x;
+      event.y = y;
       break;
     }
     case WebInputEvent::GestureTapUnconfirmed:
@@ -1994,8 +1993,8 @@ void EventSender::GestureEvent(WebInputEvent::Type type,
       } else {
         event.data.tap.tapCount = 1;
       }
-      event.x = point.x;
-      event.y = point.y;
+      event.x = x;
+      event.y = y;
       break;
     case WebInputEvent::GestureTapDown:
     {
@@ -2013,8 +2012,8 @@ void EventSender::GestureEvent(WebInputEvent::Type type,
           return;
         }
       }
-      event.x = point.x;
-      event.y = point.y;
+      event.x = x;
+      event.y = y;
       event.data.tapDown.width = width;
       event.data.tapDown.height = height;
       break;
@@ -2035,19 +2034,19 @@ void EventSender::GestureEvent(WebInputEvent::Type type,
           }
         }
       }
-      event.x = point.x;
-      event.y = point.y;
+      event.x = x;
+      event.y = y;
       event.data.showPress.width = width;
       event.data.showPress.height = height;
       break;
     }
     case WebInputEvent::GestureTapCancel:
-      event.x = point.x;
-      event.y = point.y;
+      event.x = x;
+      event.y = y;
       break;
     case WebInputEvent::GestureLongPress:
-      event.x = point.x;
-      event.y = point.y;
+      event.x = x;
+      event.y = y;
       if (!args->PeekNext().IsEmpty()) {
         float width;
         if (!args->GetNext(&width)) {
@@ -2066,8 +2065,8 @@ void EventSender::GestureEvent(WebInputEvent::Type type,
       }
       break;
     case WebInputEvent::GestureLongTap:
-      event.x = point.x;
-      event.y = point.y;
+      event.x = x;
+      event.y = y;
       if (!args->PeekNext().IsEmpty()) {
         float width;
         if (!args->GetNext(&width)) {
@@ -2086,8 +2085,8 @@ void EventSender::GestureEvent(WebInputEvent::Type type,
       }
       break;
     case WebInputEvent::GestureTwoFingerTap:
-      event.x = point.x;
-      event.y = point.y;
+      event.x = x;
+      event.y = y;
       if (!args->PeekNext().IsEmpty()) {
         float first_finger_width;
         if (!args->GetNext(&first_finger_width)) {
@@ -2123,7 +2122,7 @@ void EventSender::GestureEvent(WebInputEvent::Type type,
     WebMouseEvent mouse_event;
     InitMouseEvent(WebInputEvent::MouseDown,
                    pressed_button_,
-                   point,
+                   WebPoint(x, y),
                    GetCurrentEventTimeSec(),
                    click_count_,
                    0,