Link rel=modulepreload: Add UseCounter

Bug: 740886
Change-Id: I946c3b33aef3a1bb49ffa3e73bf1c040cbc309c0
Reviewed-on: https://chromium-review.googlesource.com/771373
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517020}

third_party/WebKit/Source/core/loader/LinkLoader.cpp

@@ -407,7 +407,7 @@ static void ModulePreloadIfNeeded(const LinkRelAttribute& rel_attribute,
   if (!document.Loader() || !rel_attribute.IsModulePreload())
     return;
 
-  // TODO(ksakamoto): add UseCounter
+  UseCounter::Count(document, WebFeature::kLinkRelModulePreload);
 
   // Step 1. "If the href attribute's value is the empty string, then return."
   // [spec text]

third_party/WebKit/public/platform/web_feature.mojom

@@ -1759,6 +1759,7 @@ enum WebFeature {
   kDocumentPageShowFired = 2229,
   kReplaceCharsetInXHR = 2230,
   kRespondToSameOriginRequestWithCrossOriginResponse = 2231,
+  kLinkRelModulePreload = 2232,
 
   // 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

@@ -16962,6 +16962,7 @@ Called by update_net_error_codes.py.-->
   <int value="2229" label="DocumentPageShowFired"/>
   <int value="2230" label="ReplaceCharsetInXHR"/>
   <int value="2231" label="RespondToSameOriginRequestWithCrossOriginResponse"/>
+  <int value="2232" label="LinkRelModulePreload"/>
 </enum>
 
 <enum name="FeedbackSource">