Add breakdown histograms for injected script execution time

extensions/renderer/script_injection.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/script_injection.h"
 
 #include <map>
 #include <utility>
 
 #include "base/lazy_instance.h"
@@ skipping 305 matching lines @@
         world_id, &sources.front(), sources.size(), is_user_gesture, option,
         callback.release());
   }
 }
 
 void ScriptInjection::OnJsInjectionCompleted(
     const std::vector<v8::Local<v8::Value>>& results,
     base::TimeDelta elapsed) {
   DCHECK(!did_inject_js_);
 
-  if (injection_host_->id().type() == HostID::EXTENSIONS)
+  if (injection_host_->id().type() == HostID::EXTENSIONS) {
     UMA_HISTOGRAM_TIMES("Extensions.InjectedScriptExecutionTime", elapsed);
+    switch (run_location_) {
+      case UserScript::DOCUMENT_START:
+        UMA_HISTOGRAM_TIMES("Extensions.InjectStart_ExecutionTime", elapsed);

[Devlin, 2017/03/21 20:40:47]

I'd recommend using a histogram suffix here, and making these, e.g.,
Extensions.InjectionExecutionTime.DocumentStart, etc.

[Kunihiko Sakamoto, 2017/03/22 07:46:34]

Ah I've forgotten about histogram_suffixes.
Done, thanks!

+        break;
+      case UserScript::DOCUMENT_END:
+        UMA_HISTOGRAM_TIMES("Extensions.InjectEnd_ExecutionTime", elapsed);
+        break;
+      case UserScript::DOCUMENT_IDLE:
+        UMA_HISTOGRAM_TIMES("Extensions.InjectIdle_ExecutionTime", elapsed);
+        break;
+      default:
+        break;
+    }
+  }
 
   bool expects_results = injector_->ExpectsResults();
   if (expects_results) {
     if (!results.empty() && !results[0].IsEmpty()) {
       // Right now, we only support returning single results (per frame).
       std::unique_ptr<content::V8ValueConverter> v8_converter(
           content::V8ValueConverter::create());
       // It's safe to always use the main world context when converting
       // here. V8ValueConverterImpl shouldn't actually care about the
       // context scope, and it switches to v8::Object's creation context
@@ skipping 21 matching lines @@
 void ScriptInjection::InjectCss(std::set<std::string>* injected_stylesheets,
                                 size_t* num_injected_stylesheets) {
   std::vector<blink::WebString> css_sources = injector_->GetCssSources(
       run_location_, injected_stylesheets, num_injected_stylesheets);
   blink::WebLocalFrame* web_frame = render_frame_->GetWebFrame();
   for (const blink::WebString& css : css_sources)
     web_frame->document().insertStyleSheet(css);
 }
 
 }  // namespace extensions