Add UMA metrics for root scroller intervention to track forcing passive breakage.

third_party/WebKit/Source/core/events/EventTargetTest.cpp

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "bindings/core/v8/ScriptController.h"
+#include "core/layout/LayoutTestHelper.h"
+#include "platform/testing/HistogramTester.h"
+
+namespace blink {
+
+enum PassiveForcedListenerResultType {
+    PreventDefaultNotCalled,
+    DocumentLevelTouchPreventDefaultCalled
+};
+
+class EventTargetTest : public RenderingTest {
+public:
+    EventTargetTest() {}
+    ~EventTargetTest() {}
+};
+
+TEST_F(EventTargetTest, PreventDefaultNotCalled)
+{
+    document().settings()->setScriptEnabled(true);
+    HistogramTester histogramTester;
+    document().frame()->script().executeScriptInMainWorld(
+        "window.addEventListener('touchstart', function(e) {}, {});"
+        "window.dispatchEvent(new TouchEvent('touchstart', {cancelable: false}));");
+
+    histogramTester.expectTotalCount(
+        "Event.PassiveForcedEventDispatchCancelled", 1);
+    histogramTester.expectUniqueSample(
+        "Event.PassiveForcedEventDispatchCancelled", PreventDefaultNotCalled, 1);
+}
+
+TEST_F(EventTargetTest, PreventDefaultCalled)
+{
+    document().settings()->setScriptEnabled(true);
+    HistogramTester histogramTester;
+    document().frame()->script().executeScriptInMainWorld(
+        "window.addEventListener('touchstart', function(e) {e.preventDefault();}, {});"
+        "window.dispatchEvent(new TouchEvent('touchstart', {cancelable: false}));");
+
+    histogramTester.expectTotalCount(
+        "Event.PassiveForcedEventDispatchCancelled", 1);
+    histogramTester.expectUniqueSample(
+        "Event.PassiveForcedEventDispatchCancelled", DocumentLevelTouchPreventDefaultCalled, 1);
+}
+
+} // namespace blink