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

extensions/renderer/binding_generating_native_handler.cc

Index: extensions/renderer/binding_generating_native_handler.cc
diff --git a/extensions/renderer/binding_generating_native_handler.cc b/extensions/renderer/binding_generating_native_handler.cc
index 8912017e7f17445468d86e097290444ad57461f2..5aa161be73fbcd927e06793c73d620caf993b221 100644
--- a/extensions/renderer/binding_generating_native_handler.cc
+++ b/extensions/renderer/binding_generating_native_handler.cc
@@ -5,6 +5,8 @@
 #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"
 
@@ -19,6 +21,7 @@ BindingGeneratingNativeHandler::BindingGeneratingNativeHandler(
     : 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|:
   //
@@ -105,6 +108,13 @@ v8::Local<v8::Object> BindingGeneratingNativeHandler::NewInstance() {
     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);
 }