StartPageService: Use a StringPiece instead of modifying a string.

chrome/browser/ui/app_list/start_page_service.cc

Index: chrome/browser/ui/app_list/start_page_service.cc
diff --git a/chrome/browser/ui/app_list/start_page_service.cc b/chrome/browser/ui/app_list/start_page_service.cc
index de3a1c33baabc09a621dff434926b8357f7743d4..9bb40fcfee593900f5201c23508b1bb579cf3863 100644
--- a/chrome/browser/ui/app_list/start_page_service.cc
+++ b/chrome/browser/ui/app_list/start_page_service.cc
@@ -12,6 +12,7 @@
 #include "base/memory/singleton.h"
 #include "base/metrics/user_metrics.h"
 #include "base/prefs/pref_service.h"
+#include "base/strings/string_piece.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/google/google_profile_helper.h"
@@ -540,10 +541,11 @@ void StartPageService::OnURLFetchComplete(const net::URLFetcher* source) {
 
   // Remove XSSI guard for JSON parsing.
   size_t json_start_index = json_data.find("{");
+  base::StringPiece json_data_substr(json_data);
   if (json_start_index != std::string::npos)
-    json_data.erase(0, json_start_index);
+    json_data_substr.remove_prefix(json_start_index);
 
-  JSONStringValueSerializer deserializer(json_data);
+  JSONStringValueSerializer deserializer(json_data_substr);
   deserializer.set_allow_trailing_comma(true);
   int error_code = 0;
   scoped_ptr<base::Value> doodle_json(