enable / disable Long Task instrumentation based on presence of LongTask observer

third_party/WebKit/Source/core/timing/PerformanceTest.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 "core/timing/Performance.h"
+
+#include "core/testing/DummyPageHolder.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace blink {
+
+class PerformanceTest : public ::testing::Test {
+protected:
+    void SetUp() override
+    {
+        m_pageHolder = DummyPageHolder::create(IntSize(800, 600));
+        m_pageHolder->document().setURL(KURL(KURL(), "https://example.com"));
+        m_performance = Performance::create(&m_pageHolder->frame());
+    }
+
+    bool hasLongTaskInspectorAgent()
+    {
+        return m_performance->m_longTaskInspectorAgent;
+    }
+
+    void addLongTaskObserver()
+    {
+        // simulate with filter options.
+        m_performance->m_observerFilterOptions |= PerformanceEntry::LongTask;
+    }
+
+    void removeLongTaskObserver()
+    {
+        // simulate with filter options.
+        m_performance->m_observerFilterOptions = PerformanceEntry::Invalid;
+    }
+
+    Persistent<Performance> m_performance;
+    std::unique_ptr<DummyPageHolder> m_pageHolder;
+};
+
+TEST_F(PerformanceTest, LongTaskObserverInstrumentation)
+{
+    m_performance->enableLongTaskInstrumentation();

[caseq, 2016/09/19 22:18:06]

Can we rather express the test in a higher-level terms, i.e. closer to the user
level -- register performance observer (or two) and check that  the long task
agent is appropriately added/removed from instrumentation?

[panicker, 2016/09/20 12:00:39]

Since I've moved this out of PerformanceObserver, I dont think it belongs in a
unittest.
This test will be added as a web-platform-test (JS).

+    EXPECT_FALSE(hasLongTaskInspectorAgent());
+
+    // Adding LongTask observer (with filer option) enables instrumentation.
+    addLongTaskObserver();
+    m_performance->enableLongTaskInstrumentation();
+    EXPECT_TRUE(hasLongTaskInspectorAgent());
+
+    // While LongTask observer is present, disableLongTaskInstrumentation has no effect.
+    m_performance->disableLongTaskInstrumentation();
+    EXPECT_TRUE(hasLongTaskInspectorAgent());
+
+    // Removing LongTask observer disables instrumentation.
+    removeLongTaskObserver();
+    m_performance->disableLongTaskInstrumentation();
+    EXPECT_FALSE(hasLongTaskInspectorAgent());
+}
+
+}