Ensure zero suggest can handle XSSI-escaped output.

chrome/browser/autocomplete/zero_suggest_provider.cc

 // Copyright (c) 2012 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/autocomplete/zero_suggest_provider.h"
 
 #include "base/callback.h"
 #include "base/i18n/case_conversion.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/metrics/histogram.h"
@@ skipping 115 matching lines @@
 void ZeroSuggestProvider::OnURLFetchComplete(const net::URLFetcher* source) {
   have_pending_request_ = false;
   LogOmniboxZeroSuggestRequest(ZERO_SUGGEST_REPLY_RECEIVED);
 
   std::string json_data;
   source->GetResponseAsString(&json_data);
   const bool request_succeeded =
       source->GetStatus().is_success() && source->GetResponseCode() == 200;
 
   if (request_succeeded) {
-    JSONStringValueSerializer deserializer(json_data);
-    deserializer.set_allow_trailing_comma(true);
-    scoped_ptr<Value> data(deserializer.Deserialize(NULL, NULL));
-    if (data.get())
-      ParseSuggestResults(*data.get());
+    // The JSON response should be an array.
+    for (size_t response_start_index = json_data.find("["), i = 0;

[H Fung, 2013/11/30 00:46:27]

I'm not sure why we try up to 5 times and why we ignore contiguous open
brackets, but I guess this works.  I'm not sure if it might be better to put
this code in a separate function in SearchProvider to avoid duplicate code?

+         response_start_index != std::string::npos && i < 5;
+         response_start_index = json_data.find("[", 1), i++) {
+      // Remove any XSSI guards to allow for JSON parsing.
+      if (response_start_index > 0)
+        json_data.erase(0, response_start_index);
+
+      JSONStringValueSerializer deserializer(json_data);
+      deserializer.set_allow_trailing_comma(true);
+      int error_code = 0;
+      scoped_ptr<Value> data(deserializer.Deserialize(&error_code, NULL));
+      if (error_code == 0) {
+        if (data.get())
+          ParseSuggestResults(*data.get());
+        break;
+      }
+    }
   }
   done_ = true;
 
   ConvertResultsToAutocompleteMatches();
   if (!matches_.empty())
     listener_->OnProviderUpdate(true);
 }
 
 void ZeroSuggestProvider::StartZeroSuggest(
     const GURL& current_page_url,
@@ skipping 304 matching lines @@
   match.is_history_what_you_typed_match = false;
   match.allowed_to_be_default_match = true;
 
   // The placeholder suggestion for the current URL has high relevance so
   // that it is in the first suggestion slot and inline autocompleted. It
   // gets dropped as soon as the user types something.
   match.relevance = verbatim_relevance_;
 
   return match;
 }