[MD Extensions] Add some performance metrics

Add some performance metrics for the MD and non-MD extensions pages so
we can begin gathering data. To start, use the signals for
DocumentLoadedInFrame() for the main frame and
DocumentOnLoadCompletedInMainFrame().

BUG=529395

Review-Url: https://codereview.chromium.org/2341553002
Cr-Commit-Position: refs/heads/master@{#418692}

chrome/browser/ui/webui/extensions/extensions_ui.cc

@@ -4,7 +4,11 @@
 
 #include "chrome/browser/ui/webui/extensions/extensions_ui.h"
 
+#include <memory>
+
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/timer/elapsed_timer.h"
 #include "build/build_config.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/profiles/profile.h"
@@ -19,6 +23,8 @@
 #include "chrome/grit/generated_resources.h"
 #include "chrome/grit/theme_resources.h"
 #include "components/google/core/browser/google_util.h"
+#include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_ui.h"
 #include "content/public/browser/web_ui_data_source.h"
 #include "extensions/common/extension_urls.h"
@@ -34,6 +40,54 @@ namespace extensions {
 
 namespace {
 
+class ExtensionWebUiTimer : public content::WebContentsObserver {
+ public:
+  explicit ExtensionWebUiTimer(content::WebContents* web_contents, bool is_md)
+      : content::WebContentsObserver(web_contents), is_md_(is_md) {}
+  ~ExtensionWebUiTimer() override {}
+
+  void DidStartProvisionalLoadForFrame(
+      content::RenderFrameHost* render_frame_host,
+      const GURL& validated_url,
+      bool is_error_page,
+      bool is_iframe_srcdoc) override {
+    timer_.reset(new base::ElapsedTimer());
+  }
+
+  void DocumentLoadedInFrame(
+      content::RenderFrameHost* render_frame_host) override {
+    if (render_frame_host != web_contents()->GetMainFrame())
+      return;
+    if (is_md_) {
+      UMA_HISTOGRAM_TIMES("Extensions.WebUi.DocumentLoadedInMainFrameTime.MD",
+                          timer_->Elapsed());
+    } else {
+      UMA_HISTOGRAM_TIMES("Extensions.WebUi.DocumentLoadedInMainFrameTime.Uber",
+                          timer_->Elapsed());
+    }
+  }
+
+  void DocumentOnLoadCompletedInMainFrame() override {
+    if (is_md_) {
+      UMA_HISTOGRAM_TIMES("Extensions.WebUi.LoadCompletedInMainFrame.MD",
+                          timer_->Elapsed());
+    } else {
+      UMA_HISTOGRAM_TIMES("Extensions.WebUi.LoadCompletedInMainFrame.Uber",
+                          timer_->Elapsed());
+    }
+  }
+
+  void WebContentsDestroyed() override { delete this; }
+
+ private:
+  // Whether this is the MD version of the chrome://extensions page.
+  bool is_md_;
+
+  std::unique_ptr<base::ElapsedTimer> timer_;
+
+  DISALLOW_COPY_AND_ASSIGN(ExtensionWebUiTimer);
+};
+
 content::WebUIDataSource* CreateMdExtensionsSource() {
   content::WebUIDataSource* source =
       content::WebUIDataSource::Create(chrome::kChromeUIExtensionsHost);
@@ -216,7 +270,10 @@ ExtensionsUI::ExtensionsUI(content::WebUI* web_ui) : WebUIController(web_ui) {
   Profile* profile = Profile::FromWebUI(web_ui);
   content::WebUIDataSource* source = nullptr;
 
-  if (base::FeatureList::IsEnabled(features::kMaterialDesignExtensions)) {
+  bool is_md =
+      base::FeatureList::IsEnabled(features::kMaterialDesignExtensions);
+
+  if (is_md) {
     source = CreateMdExtensionsSource();
     InstallExtensionHandler* install_extension_handler =
         new InstallExtensionHandler();
@@ -256,6 +313,8 @@ ExtensionsUI::ExtensionsUI(content::WebUI* web_ui) : WebUIController(web_ui) {
   }
 
   content::WebUIDataSource::Add(profile, source);
+  // Handles its own lifetime.
+  new ExtensionWebUiTimer(web_ui->GetWebContents(), is_md);
 }
 
 ExtensionsUI::~ExtensionsUI() {}

tools/metrics/histograms/histograms.xml

@@ -16938,6 +16938,25 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Extensions.WebUi.DocumentLoadedInMainFrameTime" units="ms">
+  <owner>rdevlin.cronin@chromium.org</owner>
+  <summary>
+    The amount of time between starting the provisional load and fully loading
+    the document in the main frame of the chrome://extensions page. This
+    corresponds to the WebContentsObserver::DocumentLoadedInFrame method.
+  </summary>
+</histogram>
+
+<histogram name="Extensions.WebUi.LoadCompletedInMainFrame" units="ms">
+  <owner>rdevlin.cronin@chromium.org</owner>
+  <summary>
+    The amount of time between starting the provisional load and having
+    completed the onload handler in the main frame of the chrome://extensions
+    page. This corresponds to the
+    WebContentsObserver::DocumentOnLoadCompletedInMainFrame method.
+  </summary>
+</histogram>
+
 <histogram name="ExtensionService.AddVerified" enum="BooleanSuccess">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>
@@ -101250,6 +101269,13 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="Extensions.Database.Restore"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="ExtensionWebUiPageType" separator=".">
+  <suffix name="MD" label="The Material Design chrome://extensions page."/>
+  <suffix name="Uber" label="The Uber chrome://extensions page."/>
+  <affected-histogram name="Extensions.WebUi.DocumentLoadedInMainFrameTime"/>
+  <affected-histogram name="Extensions.WebUi.LoadCompletedInMainFrame"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="ExternalExtensionEvent" separator="">
   <suffix name="NonWebstore"
       label="sideloaded extensions that don't update from the webstore"/>