Measure HTMLFrameSetElement's non-null anonymous name getter

This patch measures how often getter returns anything
other than non null.

Bug: 695891
Change-Id: I62ea96d6ccf9c0dea0804dcab221e71b55ffca37
Reviewed-on: https://chromium-review.googlesource.com/773520
Commit-Queue: Shanmuga Pandi <shanmuga.m@samsung.com>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517789}

third_party/WebKit/Source/core/html/HTMLFrameSetElement.cpp

@@ -31,6 +31,7 @@
 #include "core/events/MouseEvent.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/LocalFrameClient.h"
+#include "core/frame/UseCounter.h"
 #include "core/html/HTMLCollection.h"
 #include "core/html/HTMLFrameElement.h"
 #include "core/html_names.h"
@@ -297,7 +298,13 @@ LocalDOMWindow* HTMLFrameSetElement::AnonymousNamedGetter(
   Document* document = ToHTMLFrameElement(frame_element)->contentDocument();
   if (!document || !document->GetFrame())
     return nullptr;
-  return document->domWindow();
+
+  LocalDOMWindow* window = document->domWindow();
+  if (window) {
+    UseCounter::Count(
+        *document, WebFeature::kHTMLFrameSetElementNonNullAnonymousNamedGetter);
+  }
+  return window;
 }
 
 }  // namespace blink

third_party/WebKit/public/platform/web_feature.mojom

@@ -1760,6 +1760,7 @@ enum WebFeature {
   kLinkRelModulePreload = 2232,
   kPerformanceMeasurePassedInObject = 2233,
   kPerformanceMeasurePassedInNavigationTiming = 2234,
+  kHTMLFrameSetElementNonNullAnonymousNamedGetter = 2235,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

tools/metrics/histograms/enums.xml

@@ -16975,6 +16975,7 @@ Called by update_net_error_codes.py.-->
   <int value="2232" label="LinkRelModulePreload"/>
   <int value="2233" label="PerformanceMeasurePassedInObject"/>
   <int value="2234" label="PerformanceMeasurePassedInNavigationTiming"/>
+  <int value="2235" label="HTMLFrameSetElementNonNullAnonymousNamedGetter"/>
 </enum>
 
 <enum name="FeedbackSource">