Log to UMA when x-origin frames (1) are created and (2) become visible

third_party/WebKit/Source/core/dom/Document.cpp

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index 9879a7cc0e0173a8be94dde019fb5cb86f1c99fb..2c81a16d3b1d415fcf6316fa19bd7fe29d8328db 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -383,6 +383,21 @@ static void runAutofocusTask(ExecutionContext* context)
     }
 }
 
+// These are logged to UMA, so don't re-arrange them without creating a new histogram.
+enum DocumentVisibilityForDeferredLoading {
+    Created,
+    WouldLoadBecauseVisible,
+    // TODO(dgrogan): Add WouldLoadBecauseTopOrLeft, WouldLoadBecauseDisplayNone, etc
+
+    DocumentVisibilityForDeferredLoadingEnd
+};
+
+static void RecordStateToHistogram(DocumentVisibilityForDeferredLoading state)
+{
+    DEFINE_STATIC_LOCAL(EnumerationHistogram, unseenFrameHistogram, ("DeferredFrameLoading.StatesV1", DocumentVisibilityForDeferredLoadingEnd));
+    unseenFrameHistogram.count(state);
+}
+
 Document::Document(const DocumentInit& initializer, DocumentClassFlags documentClasses)
     : ContainerNode(0, CreateDocument)
     , TreeScope(*this)
@@ -454,6 +469,7 @@ Document::Document(const DocumentInit& initializer, DocumentClassFlags documentC
     , m_hasViewportUnits(false)
     , m_parserSyncPolicy(AllowAsynchronousParsing)
     , m_nodeCount(0)
+    , m_visibilityWasLogged(false)
 {
     if (m_frame) {
         DCHECK(m_frame->page());
@@ -484,6 +500,9 @@ Document::Document(const DocumentInit& initializer, DocumentClassFlags documentC
         setURL(initializer.url());
 
     initSecurityContext(initializer);
+    if (frame() && getSecurityOrigin() && frame()->tree().top()->securityContext() && !getSecurityOrigin()->canAccess(frame()->tree().top()->securityContext()->getSecurityOrigin()))

[dcheng, 2016/08/29 20:37:19]

I don't think securityOrigin can be null here, unless something is really
broken.

[dgrogan, 2016/08/31 19:52:41]

Good to know, changed to DCHECK.

+        RecordStateToHistogram(Created);
+
     initDNSPrefetch();
 
     InstanceCounters::incrementCounter(InstanceCounters::DocumentCounter);
@@ -6007,6 +6026,14 @@ DEFINE_TRACE(Document)
     SecurityContext::trace(visitor);
 }
 
+void Document::onVisibilityMaybeChanged(bool visible)
+{
+    if (visible && !m_visibilityWasLogged && frame() && frame()->isCrossOriginSubframe()) {

[dcheng, 2016/08/29 20:37:19]

Since frame()->document() points to this document(), frame() should not be null.
Let's just DCHECK()?

[dgrogan, 2016/08/31 19:52:41]

Done.

+        m_visibilityWasLogged = true;
+        RecordStateToHistogram(WouldLoadBecauseVisible);
+    }
+}
+
 DEFINE_TRACE_WRAPPERS(Document)
 {
     visitor->traceWrappers(m_importsController);