UseCounter: Count dynamic import usage

Bug: 711706
Change-Id: I46271b96329d45d4b2ad6ad0988490dcad98943e
Reviewed-on: https://chromium-review.googlesource.com/c/1314013
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604851}

third_party/blink/public/platform/web_feature.mojom

@@ -2065,6 +2065,7 @@ enum WebFeature {
   kSVGGeometryPropertyHasNonZeroUnitlessValue = 2613,
   kCSSValueAppearanceNoImplementationSkipBorder = 2614,
   kInstantiateModuleScript = 2615,
+  kDynamicImportModuleScript = 2616,
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.
   // Also, run update_use_counter_feature_enum.py in

third_party/blink/renderer/core/script/modulator_impl_base.cc

@@ -169,6 +169,8 @@ void ModulatorImplBase::ResolveDynamically(
         GetScriptState()->GetIsolate(), reason));
     return;
   }
+  UseCounter::Count(GetExecutionContext(),
+                    WebFeature::kDynamicImportModuleScript);
   dynamic_module_resolver_->ResolveDynamically(specifier, referrer_url,
                                                referrer_info, resolver);
 }

tools/metrics/histograms/enums.xml

@@ -20641,6 +20641,7 @@ Called by update_net_error_codes.py.-->
   <int value="2613" label="SVGGeometryPropertyHasNonZeroUnitlessValue"/>
   <int value="2614" label="CSSValueAppearanceNoImplementationSkipBorder"/>
   <int value="2615" label="InstantiateModuleScript"/>
+  <int value="2616" label="DynamicImportModuleScript"/>
 </enum>
 
 <enum name="FeaturePolicyFeature">