[Extensions] Add metrics for execution time of binding.js

extensions/renderer/binding_generating_native_handler.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "extensions/renderer/binding_generating_native_handler.h"
 
 #include "base/macros.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/timer/elapsed_timer.h"
 #include "extensions/renderer/script_context.h"
 #include "extensions/renderer/v8_helpers.h"
 
 namespace extensions {
 
 using namespace v8_helpers;
 
 BindingGeneratingNativeHandler::BindingGeneratingNativeHandler(
     ScriptContext* context,
     const std::string& api_name,
     const std::string& bind_to)
     : context_(context), api_name_(api_name), bind_to_(bind_to) {}
 
 v8::Local<v8::Object> BindingGeneratingNativeHandler::NewInstance() {
+  base::ElapsedTimer timer;
   // This long sequence of commands effectively runs the JavaScript code,
   // such that result[bind_to] is the compiled schema for |api_name|:
   //
   //   var result = {};
   //   result[bind_to] = require('binding').Binding.create(api_name).generate();
   //   return result;
   //
   // Unfortunately using the v8 APIs makes that quite verbose.
   // Each stage is marked with the code it executes.
   v8::Isolate* isolate = context_->isolate();
@@ skipping 66 matching lines @@
     NOTREACHED();
     return v8::Local<v8::Object>();
   }
 
   // var result = {};
   // result[bind_to] = ...;
   if (!SetProperty(v8_context, object, v8_bind_to, compiled_schema)) {
     NOTREACHED();
     return v8::Local<v8::Object>();
   }
+
+  // Log UMA with microsecond accuracy*; maxes at 10 seconds.
+  // *Obviously, limited by our TimeTicks implementation, but as close as
+  // possible.
+  UMA_HISTOGRAM_CUSTOM_COUNTS("Extensions.ApiBindingObjectGenerationTime",
+                              timer.Elapsed().InMicroseconds(),
+                              1, 10000000, 100);
   // return result;
   return scope.Escape(object);
 }
 
 }  // namespace extensions