[New Tab Page] Add Field Trial support to the Local NTP

chrome/browser/search/local_ntp_source.cc

 // Copyright 2013 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 "chrome/browser/search/local_ntp_source.h"
 
 #include "base/json/json_string_value_serializer.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted_memory.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/metrics/field_trial.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/values.h"
 #include "chrome/browser/search/instant_io_context.h"
 #include "chrome/browser/search/search.h"
 #include "chrome/browser/search_engines/template_url_service_factory.h"
 #include "chrome/common/url_constants.h"
 #include "components/search_engines/template_url_prepopulate_data.h"
 #include "components/search_engines/template_url_service.h"
 #include "grit/browser_resources.h"
 #include "grit/generated_resources.h"
 #include "grit/theme_resources.h"
 #include "grit/ui_resources.h"
 #include "net/url_request/url_request.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/base/webui/jstemplate_builder.h"
 #include "ui/base/webui/web_ui_util.h"
 #include "url/gurl.h"
 
 namespace {
 
+// Constants related to the new NTP design field trial.
+const char kNewNTPDesignFieldTrialName[] = "NewNTPDesign";
+const char kNewNTPDesignFieldTrialEnabledPrefix[] = "Enabled";
+
+// Class name to be used for the new design in local resources.
+const char kNewNTPDesignClassName[] = "md";
+
 // Signifies a locally constructed resource, i.e. not from grit/.
 const int kLocalResource = -1;
 
 const char kConfigDataFilename[] = "config.js";
+const char kLocalNTPFilename[] = "local-ntp.html";
 
 const struct Resource{
   const char* filename;
   int identifier;
   const char* mime_type;
 } kResources[] = {
-  { "local-ntp.html", IDR_LOCAL_NTP_HTML, "text/html" },
+  { kLocalNTPFilename, IDR_LOCAL_NTP_HTML, "text/html" },
   { "local-ntp.js", IDR_LOCAL_NTP_JS, "application/javascript" },
   { kConfigDataFilename, kLocalResource, "application/javascript" },
   { "local-ntp.css", IDR_LOCAL_NTP_CSS, "text/css" },
   { "images/close_2.png", IDR_CLOSE_2, "image/png" },
   { "images/close_2_hover.png", IDR_CLOSE_2_H, "image/png" },
   { "images/close_2_active.png", IDR_CLOSE_2_P, "image/png" },
   { "images/close_2_white.png", IDR_CLOSE_2_MASK, "image/png" },
   { "images/google_logo.png", IDR_LOCAL_NTP_IMAGES_LOGO_PNG, "image/png" },
   { "images/white_google_logo.png",
     IDR_LOCAL_NTP_IMAGES_WHITE_LOGO_PNG, "image/png" },
@@ skipping 14 matching lines @@
     return false;
 
   const TemplateURL* default_provider =
       template_url_service->GetDefaultSearchProvider();
   return default_provider &&
       (TemplateURLPrepopulateData::GetEngineType(
           *default_provider, template_url_service->search_terms_data()) ==
        SEARCH_ENGINE_GOOGLE);
 }
 
+// Returns whether the user is part of a group where the new NTP design is
+// enabled.
+bool IsNewDesignEnabled() {
+  return StartsWithASCII(
+      base::FieldTrialList::FindFullName(kNewNTPDesignFieldTrialName),
+      kNewNTPDesignFieldTrialEnabledPrefix, true);
+}
+
 // Adds a localized string keyed by resource id to the dictionary.
 void AddString(base::DictionaryValue* dictionary,
                const std::string& key,
                int resource_id) {
   dictionary->SetString(key, l10n_util::GetStringUTF16(resource_id));
 }
 
 // Populates |translated_strings| dictionary for the local NTP.
 scoped_ptr<base::DictionaryValue> GetTranslatedStrings() {
   scoped_ptr<base::DictionaryValue> translated_strings(
@@ skipping 55 matching lines @@
     const std::string& path,
     int render_process_id,
     int render_frame_id,
     const content::URLDataSource::GotDataCallback& callback) {
   const std::string stripped_path = StripParameters(path);
   if (stripped_path == kConfigDataFilename) {
     std::string config_data_js = GetConfigData(profile_);
     callback.Run(base::RefCountedString::TakeString(&config_data_js));
     return;
   }
+  if (stripped_path == kLocalNTPFilename) {
+    SendResourceWithClass(
+        IDR_LOCAL_NTP_HTML, IsNewDesignEnabled() ? kNewNTPDesignClassName : "",
+        callback);
+    return;
+  }
   float scale = 1.0f;
   std::string filename;
   webui::ParsePathAndScale(
       GURL(GetLocalNtpPath() + stripped_path), &filename, &scale);
   ui::ScaleFactor scale_factor = ui::GetSupportedScaleFactor(scale);
   for (size_t i = 0; i < arraysize(kResources); ++i) {
     if (filename == kResources[i].filename) {
       scoped_refptr<base::RefCountedStaticMemory> response(
           ResourceBundle::GetSharedInstance().LoadDataResourceBytesForScale(
               kResources[i].identifier, scale_factor));
@@ skipping 29 matching lines @@
     }
   }
   return false;
 }
 
 std::string LocalNtpSource::GetContentSecurityPolicyFrameSrc() const {
   // Allow embedding of most visited iframes.
   return base::StringPrintf("frame-src %s;",
                             chrome::kChromeSearchMostVisitedUrl);
 }
+
+void LocalNtpSource::SendResourceWithClass(
+    int resource_id,
+    const std::string& class_name,
+    const content::URLDataSource::GotDataCallback& callback) {
+  base::StringPiece resource_data =
+      ResourceBundle::GetSharedInstance().GetRawDataResource(resource_id);
+  std::string response(resource_data.as_string());
+  ReplaceFirstSubstringAfterOffset(&response, 0, "{{CLASS}}", class_name);
+  callback.Run(base::RefCountedString::TakeString(&response));
+}