Put LayoutAnalyzer back behind disabled-by-default-blink.debug.layout.

Source/core/frame/FrameView.cpp

Index: Source/core/frame/FrameView.cpp
diff --git a/Source/core/frame/FrameView.cpp b/Source/core/frame/FrameView.cpp
index 957f41cbf5f5c4b1a7da913de325bd673447235d..74e23dc96c9f96b191802d21986146f5ae768365 100644
--- a/Source/core/frame/FrameView.cpp
+++ b/Source/core/frame/FrameView.cpp
@@ -812,9 +812,24 @@ static inline void layoutFromRootObject(LayoutObject& root)
     root.layout();
 }
 
+void FrameView::prepareLayoutAnalyzer()
+{
+    bool isTracing = false;
+    TRACE_EVENT_CATEGORY_GROUP_ENABLED(TRACE_DISABLED_BY_DEFAULT("blink.debug.layout"), &isTracing);
+    if (!isTracing) {
+        m_analyzer.clear();
+        return;
+    }
+    if (!m_analyzer)
+        m_analyzer = adoptPtr(new LayoutAnalyzer());
+    m_analyzer->reset();
+}
+
 PassRefPtr<TracedValue> FrameView::analyzerCounters()
 {
-    RefPtr<TracedValue> value = layoutAnalyzer().toTracedValue();
+    if (!m_analyzer)
+        return TracedValue::create();
+    RefPtr<TracedValue> value = m_analyzer->toTracedValue();
     value->setString("host", layoutView()->document().location()->host());
     return value;
 }
@@ -826,7 +841,7 @@ void FrameView::performLayout(bool inSubtreeLayout)
     ASSERT(inSubtreeLayout || m_layoutSubtreeRoots.isEmpty());
 
     TRACE_EVENT_BEGIN0(PERFORM_LAYOUT_TRACE_CATEGORIES, "FrameView::performLayout");
-    layoutAnalyzer().reset();
+    prepareLayoutAnalyzer();
 
     ScriptForbiddenScope forbidScript;
 
@@ -842,7 +857,8 @@ void FrameView::performLayout(bool inSubtreeLayout)
     forceLayoutParentViewIfNeeded();
 
     if (inSubtreeLayout) {
-        layoutAnalyzer().increment(LayoutAnalyzer::PerformLayoutRootLayoutObjects, m_layoutSubtreeRoots.size());
+        if (m_analyzer)
+            m_analyzer->increment(LayoutAnalyzer::PerformLayoutRootLayoutObjects, m_layoutSubtreeRoots.size());
         while (m_layoutSubtreeRoots.size()) {
             LayoutObject& root = *m_layoutSubtreeRoots.takeAny();
             if (!root.needsLayout())
@@ -863,7 +879,8 @@ void FrameView::performLayout(bool inSubtreeLayout)
 
     lifecycle().advanceTo(DocumentLifecycle::AfterPerformLayout);
 
-    layoutAnalyzer().recordCounters();
+    if (m_analyzer)
+        m_analyzer->recordCounters();
     TRACE_EVENT_END1(PERFORM_LAYOUT_TRACE_CATEGORIES, "FrameView::performLayout",
         "counters", analyzerCounters());
 }