UseCounter: Count ES6 modules instantiation

This should serve as a better proxy for measuring ES6 modules usage
in the wild.
Before this CL, we relied on kPrepareModuleScript, which only counts
ES6 module usage via <script type=module>, and no other invocation paths.
kInstantiateModuleScript will also cover module usage via dynamic import,
via workers, and others.

Bug: 594639
Change-Id: I5d1690fcfb7ea6ee9eac3beb22a4659a1410c561
Reviewed-on: https://chromium-review.googlesource.com/c/1314011Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604842}

third_party/blink/public/platform/web_feature.mojom

@@ -2064,6 +2064,7 @@ enum WebFeature {
   kV8OptimizedFunctionWithOneShotBytecode = 2612,
   kSVGGeometryPropertyHasNonZeroUnitlessValue = 2613,
   kCSSValueAppearanceNoImplementationSkipBorder = 2614,
+  kInstantiateModuleScript = 2615,
   // 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

@@ -7,6 +7,7 @@
 #include "third_party/blink/public/platform/task_type.h"
 #include "third_party/blink/renderer/bindings/core/v8/script_promise_resolver.h"
 #include "third_party/blink/renderer/core/execution_context/execution_context.h"
+#include "third_party/blink/renderer/core/frame/use_counter.h"
 #include "third_party/blink/renderer/core/loader/modulescript/module_script_fetch_request.h"
 #include "third_party/blink/renderer/core/loader/modulescript/module_tree_linker.h"
 #include "third_party/blink/renderer/core/loader/modulescript/module_tree_linker_registry.h"
@@ -189,6 +190,9 @@ ModuleImportMeta ModulatorImplBase::HostGetImportMetaProperties(
 }
 
 ScriptValue ModulatorImplBase::InstantiateModule(ScriptModule script_module) {
+  UseCounter::Count(GetExecutionContext(),
+                    WebFeature::kInstantiateModuleScript);
+
   ScriptState::Scope scope(script_state_);
   return script_module.Instantiate(script_state_);
 }

tools/metrics/histograms/enums.xml

@@ -20640,6 +20640,7 @@ Called by update_net_error_codes.py.-->
   <int value="2612" label="V8OptimizedFunctionWithOneShotBytecode"/>
   <int value="2613" label="SVGGeometryPropertyHasNonZeroUnitlessValue"/>
   <int value="2614" label="CSSValueAppearanceNoImplementationSkipBorder"/>
+  <int value="2615" label="InstantiateModuleScript"/>
 </enum>
 
 <enum name="FeaturePolicyFeature">