Add breakdown histograms for injected script execution time

extensions/renderer/script_injection.cc

Index: extensions/renderer/script_injection.cc
diff --git a/extensions/renderer/script_injection.cc b/extensions/renderer/script_injection.cc
index 519dce0ba520efa0ae83a0ab0ad8b745364942e7..cd7da1bbbf78a4db4c6db0f5bf6ff320242802f7 100644
--- a/extensions/renderer/script_injection.cc
+++ b/extensions/renderer/script_injection.cc
@@ -323,8 +323,25 @@ void ScriptInjection::OnJsInjectionCompleted(
     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.InjectedScriptExecutionTime.DocumentStart", elapsed);
+        break;
+      case UserScript::DOCUMENT_END:
+        UMA_HISTOGRAM_TIMES(
+            "Extensions.InjectedScriptExecutionTime.DocumentEnd", elapsed);
+        break;
+      case UserScript::DOCUMENT_IDLE:
+        UMA_HISTOGRAM_TIMES(
+            "Extensions.InjectedScriptExecutionTime.DocumentIdle", elapsed);
+        break;
+      default:
+        break;
+    }
+  }
 
   bool expects_results = injector_->ExpectsResults();
   if (expects_results) {