Improve New Tab Page load performance.

This change nets another 65ms (20%) improvement in the duration between the
renderer requesting the NTP and it having all of the resources for the NTP
available and being completely done with layout on my Mac laptop in release
mode.

Move the handling of important resource requests needed for NTP layout from the
UI thread onto the IO thread.  This is handled by caching the necessary data on
the UI thread when possible, so that no profile or theme access is needed to
service the request.  There is often a lot of contention for the UI thread when
a new tab is created, and allowing these requests to be handled more directly
by the IO thread allows the renderer to lay the page out while the browser is
still busy doing UI work.

http://groups.google.com/group/chromium-dev/browse_thread/thread/7148074f807dc5f7

TEST=Do the new tab page and new incognito tab page still work?
     Are they faster?
BUG=13337
Review URL: http://codereview.chromium.org/179069

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@25232 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 83 insertions, 39 deletions

diff --git a/chrome/browser/dom_ui/new_tab_ui.cc b/chrome/browser/dom_ui/new_tab_ui.cc
index 95b976d..dfb97ba 100644
--- a/chrome/browser/dom_ui/new_tab_ui.cc
+++ b/chrome/browser/dom_ui/new_tab_ui.cc
@@ -200,6 +200,14 @@ class NewTabHTMLSource : public ChromeURLDataManager::DataSource {
     return "text/html";
   }
 
+  virtual MessageLoop* MessageLoopForRequestPath(const std::string& path)
+      const {
+    // NewTabHTMLSource does all of the operations that need to be on the
+    // UI thread from InitFullHTML, called by the constructor.  It is safe
+    // to call StartDataRequest from any thread, so return NULL.
+    return NULL;
+  }
+
   // Setters and getters for first_view.
   static void set_first_view(bool first_view) { first_view_ = first_view; }
   static bool first_view() { return first_view_; }
@@ -214,6 +222,17 @@ class NewTabHTMLSource : public ChromeURLDataManager::DataSource {
   // string in case of failure.
   static std::string GetCustomNewTabPageFromCommandLine();
 
+  // Populate full_html_.  This must be called from the UI thread because it
+  // involves profile access.
+  //
+  // A new NewTabHTMLSource object is used for each new tab page instance
+  // and each reload of an existing new tab page, so there is no concern
+  // about cached data becoming stale.
+  void InitFullHTML();
+
+  // The content to be served by StartDataRequest, stored by InitFullHTML.
+  std::string full_html_;
+
   // Whether this is the first viewing of the new tab page and
   // we think it is the user's startup page.
   static bool first_view_;
@@ -234,6 +253,7 @@ bool NewTabHTMLSource::first_run_ = true;
 NewTabHTMLSource::NewTabHTMLSource(Profile* profile)
     : DataSource(chrome::kChromeUINewTabHost, MessageLoop::current()),
       profile_(profile) {
+  InitFullHTML();
 }
 
 void NewTabHTMLSource::StartDataRequest(const std::string& path,
@@ -245,6 +265,35 @@ void NewTabHTMLSource::StartDataRequest(const std::string& path,
     return;
   }
 
+  scoped_refptr<RefCountedBytes> html_bytes(new RefCountedBytes);
+  html_bytes->data.resize(full_html_.size());
+  std::copy(full_html_.begin(), full_html_.end(), html_bytes->data.begin());
+
+  SendResponse(request_id, html_bytes);
+}
+
+// static
+std::string NewTabHTMLSource::GetCustomNewTabPageFromCommandLine() {
+  const CommandLine* command_line = CommandLine::ForCurrentProcess();
+  const std::wstring file_path_wstring = command_line->GetSwitchValue(
+      switches::kNewTabPage);
+
+#if defined(OS_WIN)
+  const FilePath::StringType file_path = file_path_wstring;
+#else
+  const FilePath::StringType file_path = WideToASCII(file_path_wstring);
+#endif
+
+  if (!file_path.empty()) {
+    std::string file_contents;
+    if (file_util::ReadFileToString(FilePath(file_path), &file_contents))
+      return file_contents;
+  }
+
+  return std::string();
+}
+
+void NewTabHTMLSource::InitFullHTML() {
   // Show the profile name in the title and most visited labels if the current
   // profile is not the default.
   std::wstring title;
@@ -383,37 +432,10 @@ void NewTabHTMLSource::StartDataRequest(const std::string& path,
             IDR_NEW_NEW_TAB_HTML);
   }
 
-  std::string full_html(new_tab_html.data(), new_tab_html.size());
-  jstemplate_builder::AppendJsonHtml(&localized_strings, &full_html);
-  jstemplate_builder::AppendI18nTemplateSourceHtml(&full_html);
-  jstemplate_builder::AppendI18nTemplateProcessHtml(&full_html);
-
-  scoped_refptr<RefCountedBytes> html_bytes(new RefCountedBytes);
-  html_bytes->data.resize(full_html.size());
-  std::copy(full_html.begin(), full_html.end(), html_bytes->data.begin());
-
-  SendResponse(request_id, html_bytes);
-}
-
-// static
-std::string NewTabHTMLSource::GetCustomNewTabPageFromCommandLine() {
-  const CommandLine* command_line = CommandLine::ForCurrentProcess();
-  const std::wstring file_path_wstring = command_line->GetSwitchValue(
-      switches::kNewTabPage);
-
-#if defined(OS_WIN)
-  const FilePath::StringType file_path = file_path_wstring;
-#else
-  const FilePath::StringType file_path = WideToASCII(file_path_wstring);
-#endif
-
-  if (!file_path.empty()) {
-    std::string file_contents;
-    if (file_util::ReadFileToString(FilePath(file_path), &file_contents))
-      return file_contents;
-  }
-
-  return std::string();
+  full_html_.assign(new_tab_html.data(), new_tab_html.size());
+  jstemplate_builder::AppendJsonHtml(&localized_strings, &full_html_);
+  jstemplate_builder::AppendI18nTemplateSourceHtml(&full_html_);
+  jstemplate_builder::AppendI18nTemplateProcessHtml(&full_html_);
 }
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -432,7 +454,26 @@ class IncognitoTabHTMLSource : public ChromeURLDataManager::DataSource {
     return "text/html";
   }
 
+  virtual MessageLoop* MessageLoopForRequestPath(const std::string& path)
+      const {
+    // IncognitoTabHTMLSource does all of the operations that need to be on
+    // the UI thread from InitFullHTML, called by the constructor.  It is safe
+    // to call StartDataRequest from any thread, so return NULL.
+    return NULL;
+  }
+
  private:
+  // Populate full_html_.  This must be called from the UI thread because it
+  // involves profile access.
+  //
+  // A new IncognitoTabHTMLSource object is used for each incognito tab page
+  // instance and each reload of an existing incognito tab page, so there is
+  // no concern about cached data becoming stale.
+  void InitFullHTML();
+
+  // The content to be served by StartDataRequest, stored by InitFullHTML.
+  std::string full_html_;
+
   bool bookmark_bar_attached_;
 
   DISALLOW_COPY_AND_ASSIGN(IncognitoTabHTMLSource);
@@ -441,10 +482,19 @@ class IncognitoTabHTMLSource : public ChromeURLDataManager::DataSource {
 IncognitoTabHTMLSource::IncognitoTabHTMLSource(bool bookmark_bar_attached)
     : DataSource(chrome::kChromeUINewTabHost, MessageLoop::current()),
       bookmark_bar_attached_(bookmark_bar_attached) {
+  InitFullHTML();
 }
 
 void IncognitoTabHTMLSource::StartDataRequest(const std::string& path,
                                               int request_id) {
+  scoped_refptr<RefCountedBytes> html_bytes(new RefCountedBytes);
+  html_bytes->data.resize(full_html_.size());
+  std::copy(full_html_.begin(), full_html_.end(), html_bytes->data.begin());
+
+  SendResponse(request_id, html_bytes);
+}
+
+void IncognitoTabHTMLSource::InitFullHTML() {
   DictionaryValue localized_strings;
   localized_strings.SetString(L"title",
       l10n_util::GetString(IDS_NEW_TAB_TITLE));
@@ -460,14 +510,8 @@ void IncognitoTabHTMLSource::StartDataRequest(const std::string& path,
       ResourceBundle::GetSharedInstance().GetRawDataResource(
           IDR_INCOGNITO_TAB_HTML));
 
-  const std::string full_html = jstemplate_builder::GetI18nTemplateHtml(
-      incognito_tab_html, &localized_strings);
-
-  scoped_refptr<RefCountedBytes> html_bytes(new RefCountedBytes);
-  html_bytes->data.resize(full_html.size());
-  std::copy(full_html.begin(), full_html.end(), html_bytes->data.begin());
-
-  SendResponse(request_id, html_bytes);
+  full_html_ = jstemplate_builder::GetI18nTemplateHtml(incognito_tab_html,
+                                                       &localized_strings);
 }
 
 ///////////////////////////////////////////////////////////////////////////////