Track frame context URL using first script heuristic

third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp

Index: third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp
diff --git a/third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp b/third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp
index ad4732b0535a11de6d56e0d585d9b953eb97cfea..3e085f1dad921f58b49bdf0dda7b619061c1993c 100644
--- a/third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp
+++ b/third_party/WebKit/Source/core/inspector/InspectorWebPerfAgent.cpp
@@ -4,22 +4,39 @@
 
 #include "core/inspector/InspectorWebPerfAgent.h"
 
+#include "core/dom/Document.h"
+#include "core/dom/ExecutionContext.h"
 #include "core/frame/LocalFrame.h"
+#include "core/frame/Location.h"
 #include "core/inspector/InspectedFrames.h"
+#include "public/platform/Platform.h"
 
 namespace blink {
 
 InspectorWebPerfAgent::InspectorWebPerfAgent(InspectedFrames* inspectedFrames)
     : m_inspectedFrames(inspectedFrames)
 {
+    Platform::current()->currentThread()->addTaskTimeObserver(this);
+    Platform::current()->currentThread()->addTaskObserver(this);
 }
 
 InspectorWebPerfAgent::~InspectorWebPerfAgent()
 {
+    Platform::current()->currentThread()->removeTaskTimeObserver(this);
+    Platform::current()->currentThread()->removeTaskObserver(this);
 }
 
 void InspectorWebPerfAgent::willExecuteScript(ExecutionContext* context)
 {
+    // Heuristic for minimal frame context attribution: note the Location URL
+    // for each script execution. When a long task is encountered,
+    // if there is only one Location URL involved, then report it.
+    // Otherwise don't report Location URL.
+    // NOTE: This heuristic is imperfect and will be improved in V2 API.
+    // In V2, timing of script execution along with style & layout updates will be
+    // accounted for detailed and more accurate attribution.
+    if (context->isDocument())
+        m_frameContextLocations.add(toDocument(context)->location());
 }
 
 void InspectorWebPerfAgent::didExecuteScript()
@@ -28,6 +45,9 @@ void InspectorWebPerfAgent::didExecuteScript()
 
 void InspectorWebPerfAgent::willProcessTask()
 {
+    // Reset m_frameContextLocations. We don't clear this in didProcessTask
+    // as it is needed in ReportTaskTime which occurs after didProcessTask.
+    m_frameContextLocations.clear();
 }
 
 void InspectorWebPerfAgent::didProcessTask()
@@ -41,6 +61,7 @@ void InspectorWebPerfAgent::ReportTaskTime(double startTime, double endTime)
 DEFINE_TRACE(InspectorWebPerfAgent)
 {
     visitor->trace(m_inspectedFrames);
+    visitor->trace(m_frameContextLocations);
 }
 
 } // namespace blink