Add console warning for canceling uncancelable TouchEvent

Source/core/events/TouchEvent.cpp

Index: Source/core/events/TouchEvent.cpp
diff --git a/Source/core/events/TouchEvent.cpp b/Source/core/events/TouchEvent.cpp
index f252c9a155de4d8f7ae1a1d6ad339e77be6bbb3e..6c28ef62ec1011334c9988789201df4f271e7028 100644
--- a/Source/core/events/TouchEvent.cpp
+++ b/Source/core/events/TouchEvent.cpp
@@ -29,6 +29,8 @@
 #include "core/events/TouchEvent.h"
 
 #include "core/events/EventDispatcher.h"
+#include "core/frame/FrameConsole.h"
+#include "core/frame/LocalFrame.h"
 
 namespace WebCore {
 
@@ -91,6 +93,18 @@ bool TouchEvent::isTouchEvent() const
     return true;
 }
 
+void TouchEvent::preventDefault()
+{
+    MouseRelatedEvent::preventDefault();
+
+    if (!cancelable()) {

[pfeldman, 2014/05/07 15:36:21]

Blink's recommendation is to stack guard expressions instead of nested
conditions.

+        LocalFrame* frame = view() ? view()->frame() : 0;
+        if (frame) {
+            frame->console().addMessage(JSMessageSource, WarningMessageLevel,
+                "Ignored attempt to cancel a " + type() + " event with cancelable=false, for example because scrolling is in progress and cannot be interrupted.");
+        }
+    }
+}
 void TouchEvent::trace(Visitor* visitor)
 {
     visitor->trace(m_touches);