PerformanceMonitor: do not maintain a vector of frames in the monitor, single ExecutionContext memb…

third_party/WebKit/Source/core/timing/Performance.cpp

Index: third_party/WebKit/Source/core/timing/Performance.cpp
diff --git a/third_party/WebKit/Source/core/timing/Performance.cpp b/third_party/WebKit/Source/core/timing/Performance.cpp
index da6233deabda0ef21a4bcfdd3698f09c0923d35d..81fa3b2a984d8f28fb96183d10beb72412e1038c 100644
--- a/third_party/WebKit/Source/core/timing/Performance.cpp
+++ b/third_party/WebKit/Source/core/timing/Performance.cpp
@@ -166,19 +166,21 @@ static bool canAccessOrigin(Frame* frame1, Frame* frame2) {
  */
 // static
 std::pair<String, DOMWindow*> Performance::sanitizedAttribution(
-    const HeapHashSet<Member<Frame>>& frames,
+    ExecutionContext* taskContext,
+    bool hasMultipleContexts,
     Frame* observerFrame) {
-  if (frames.size() == 0) {
+  if (!taskContext || !taskContext->isDocument() ||

[caseq, 2016/12/01 02:32:46]

This will result in always returning kUnknownAttribution instead of
kAmbiguousAttribution (can you fix the typo as a drive by btw?)

+      !toDocument(taskContext)->frame()) {
     // Unable to attribute as no script was involved.
     return std::make_pair(kUnknownAttribution, nullptr);
   }
-  if (frames.size() > 1) {
+  if (hasMultipleContexts) {
     // Unable to attribute, multiple script execution contents were involved.
     return std::make_pair(kAmbugiousAttribution, nullptr);
   }
+
   // Exactly one culprit location, attribute based on origin boundary.
-  DCHECK_EQ(1u, frames.size());
-  Frame* culpritFrame = *frames.begin();
+  Frame* culpritFrame = toDocument(taskContext)->frame();
   DCHECK(culpritFrame);
   if (canAccessOrigin(observerFrame, culpritFrame)) {
     // From accessible frames or same origin, return culprit location URL.
@@ -208,12 +210,12 @@ std::pair<String, DOMWindow*> Performance::sanitizedAttribution(
   return std::make_pair(kCrossOriginAttribution, nullptr);
 }
 
-void Performance::reportLongTask(
-    double startTime,
-    double endTime,
-    const HeapHashSet<Member<Frame>>& contextFrames) {
-  std::pair<String, DOMWindow*> attribution =
-      Performance::sanitizedAttribution(contextFrames, frame());
+void Performance::reportLongTask(double startTime,
+                                 double endTime,
+                                 ExecutionContext* taskContext,
+                                 bool hasMultipleContexts) {
+  std::pair<String, DOMWindow*> attribution = Performance::sanitizedAttribution(
+      taskContext, hasMultipleContexts, frame());
   DOMWindow* culpritDomWindow = attribution.second;
   if (!culpritDomWindow || !culpritDomWindow->document() ||
       !culpritDomWindow->document()->localOwner()) {