Instrument calls to navigator.mimeTypes.

This will be used to analyze how much entropy leaked by this API can be
used for cross-site tracking.

Bug: 973801
Change-Id: I1691fb17d2da0268ce77617a00309ae3f5b9f92f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2442894Reviewed-by: Asanka Herath <asanka@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Chris Fredrickson <cfredric@google.com>
Auto-Submit: Chris Fredrickson <cfredric@google.com>
Cr-Commit-Position: refs/heads/master@{#813778}

third_party/blink/renderer/modules/plugins/navigator_plugins.cc

@@ -10,6 +10,7 @@
 #include "third_party/blink/renderer/core/frame/local_frame.h"
 #include "third_party/blink/renderer/core/frame/navigator.h"
 #include "third_party/blink/renderer/core/frame/settings.h"
+#include "third_party/blink/renderer/modules/plugins/dom_mime_type.h"
 #include "third_party/blink/renderer/modules/plugins/dom_mime_type_array.h"
 #include "third_party/blink/renderer/modules/plugins/dom_plugin_array.h"
 #include "third_party/blink/renderer/platform/privacy_budget/identifiability_digest_helpers.h"
@@ -91,11 +92,40 @@ DOMPluginArray* NavigatorPlugins::plugins(LocalFrame* frame) const {
 }
 
 DOMMimeTypeArray* NavigatorPlugins::mimeTypes(LocalFrame* frame) const {
-  if (!mime_types_)
+  if (!mime_types_) {
     mime_types_ = MakeGarbageCollected<DOMMimeTypeArray>(frame);
+    RecordMimeTypes(frame);
+  }
   return mime_types_.Get();
 }
 
+void NavigatorPlugins::RecordMimeTypes(LocalFrame* frame) const {
+  constexpr IdentifiableSurface surface = IdentifiableSurface::FromTypeAndToken(
+      IdentifiableSurface::Type::kWebFeature, WebFeature::kNavigatorMimeTypes);
+  if (!IdentifiabilityStudySettings::Get()->IsSurfaceAllowed(surface) || !frame)
+    return;
+  Document* document = frame->GetDocument();
+  if (!document)
+    return;
+  IdentifiableTokenBuilder builder;
+  for (unsigned i = 0; i < mime_types_->length(); i++) {
+    DOMMimeType* mime_type = mime_types_->item(i);
+    builder.AddToken(IdentifiabilityBenignStringToken(mime_type->type()));
+    builder.AddToken(
+        IdentifiabilityBenignStringToken(mime_type->description()));
+    builder.AddToken(IdentifiabilityBenignStringToken(mime_type->suffixes()));
+    DOMPlugin* plugin = mime_type->enabledPlugin();
+    if (plugin) {
+      builder.AddToken(IdentifiabilityBenignStringToken(plugin->name()));
+      builder.AddToken(IdentifiabilityBenignStringToken(plugin->filename()));
+      builder.AddToken(IdentifiabilityBenignStringToken(plugin->description()));
+    }
+  }
+  IdentifiabilityMetricBuilder(document->UkmSourceID())
+      .Set(surface, builder.GetToken())
+      .Record(document->UkmRecorder());
+}
+
 void NavigatorPlugins::Trace(Visitor* visitor) const {
   visitor->Trace(plugins_);
   visitor->Trace(mime_types_);

third_party/blink/renderer/modules/plugins/navigator_plugins.h

@@ -35,6 +35,8 @@ class NavigatorPlugins final : public GarbageCollected<NavigatorPlugins>,
   DOMPluginArray* plugins(LocalFrame*) const;
   DOMMimeTypeArray* mimeTypes(LocalFrame*) const;
 
+  void RecordMimeTypes(LocalFrame*) const;
+
   mutable Member<DOMPluginArray> plugins_;
   mutable Member<DOMMimeTypeArray> mime_types_;
 };