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

chrome/browser/search/local_ntp_source.cc

Index: chrome/browser/search/local_ntp_source.cc
diff --git a/chrome/browser/search/local_ntp_source.cc b/chrome/browser/search/local_ntp_source.cc
index bcda9f437e71d5f5b2fdb3b2b7e4f7cbd13daf4a..7f3f920f281b8b1060475aef58b4e1faf53f49f3 100644
--- a/chrome/browser/search/local_ntp_source.cc
+++ b/chrome/browser/search/local_ntp_source.cc
@@ -8,6 +8,7 @@
 #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"
@@ -30,17 +31,25 @@
 
 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" },
@@ -75,6 +84,14 @@ bool DefaultSearchProviderIsGoogle(Profile* profile) {
        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,
@@ -150,6 +167,12 @@ void LocalNtpSource::StartDataRequest(
     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(
@@ -199,3 +222,14 @@ std::string LocalNtpSource::GetContentSecurityPolicyFrameSrc() const {
   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));
+}