Bug 790732 - Components shim telemetry. r=mrbkap

dom/base/nsDOMClassInfo.cpp

@@ -5209,6 +5209,9 @@ const InterfaceShimEntry kInterfaceShimMap[] =
 static nsresult
 DefineComponentsShim(JSContext *cx, JS::HandleObject global)
 {
+  // Keep track of how often this happens.
+  Telemetry::Accumulate(Telemetry::COMPONENTS_SHIM_ACCESSED_BY_CONTENT, true);
+
   // Create a fake Components object.
   JSObject *components = JS_NewObject(cx, nullptr, nullptr, global);
   NS_ENSURE_TRUE(components, NS_ERROR_OUT_OF_MEMORY);

toolkit/components/telemetry/Histograms.json

@@ -2895,6 +2895,10 @@
     "kind": "flag",
     "description": "Whether content ever accesed Components.interfaces in this session"
   },
+  "COMPONENTS_SHIM_ACCESSED_BY_CONTENT": {
+    "kind": "flag",
+    "description": "Whether content ever accesed the Components shim in this session"
+  },
   "CHECK_ADDONS_MODIFIED_MS": {
     "kind": "exponential",
     "high": "5000",