diff --git a/content/shell/renderer/test_runner/web_test_proxy.cc b/content/shell/renderer/test_runner/web_test_proxy.cc
index 6a50df3..989502b 100644
--- a/content/shell/renderer/test_runner/web_test_proxy.cc
+++ b/content/shell/renderer/test_runner/web_test_proxy.cc
@@ -9,6 +9,7 @@
 #include "base/callback_helpers.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
+#include "base/strings/stringprintf.h"
 #include "content/shell/renderer/test_runner/MockWebSpeechRecognizer.h"
 #include "content/shell/renderer/test_runner/SpellCheckClient.h"
 #include "content/shell/renderer/test_runner/TestCommon.h"
@@ -114,12 +115,10 @@
     delegate->printMessage("(null)");
     return;
   }
-  std::string url = response.url().spec();
-  char data[100];
-  snprintf(data, sizeof(data), "%d", response.httpStatusCode());
-  delegate->printMessage(std::string("<NSURLResponse ") +
-                         DescriptionSuitableForTestResult(url) +
-                         ", http status code " + data + ">");
+  delegate->printMessage(base::StringPrintf(
+      "<NSURLResponse %s, http status code %d>",
+      DescriptionSuitableForTestResult(response.url().spec()).c_str(),
+      response.httpStatusCode()));
 }
 
 std::string URLDescription(const GURL& url) {
@@ -286,10 +285,8 @@
       result =
           std::string("frame '") + frame->uniqueName().utf8().data() + "' ";
     }
-    char data[100];
-    snprintf(
-        data, sizeof(data), "scrolled to %d,%d\n", offset.width, offset.height);
-    result += data;
+    base::StringAppendF(
+        &result, "scrolled to %d,%d\n", offset.width, offset.height);
   }
 
   if (!recursive)
@@ -964,12 +961,8 @@
     unsigned pendingUnloadEvents = frame->unloadListenerCount();
     if (pendingUnloadEvents) {
       PrintFrameDescription(delegate_, frame);
-      char buffer[100];
-      snprintf(buffer,
-               sizeof(buffer),
-               " - has %u onunload handler(s)\n",
-               pendingUnloadEvents);
-      delegate_->printMessage(buffer);
+      delegate_->printMessage(base::StringPrintf(
+          " - has %u onunload handler(s)\n", pendingUnloadEvents));
     }
   }
 }
@@ -1136,13 +1129,10 @@
       delegate_->printMessage("<unknown>");
     else
       delegate_->printMessage(resource_identifier_map_[identifier]);
-    delegate_->printMessage(" changed priority to ");
-    delegate_->printMessage(PriorityDescription(priority));
-    char buffer[64];
-    snprintf(
-        buffer, sizeof(buffer), ", intra_priority %d", intra_priority_value);
-    delegate_->printMessage(buffer);
-    delegate_->printMessage("\n");
+    delegate_->printMessage(
+        base::StringPrintf(" changed priority to %s, intra_priority %d\n",
+                           PriorityDescription(priority).c_str(),
+                           intra_priority_value));
   }
 }
 
@@ -1186,9 +1176,7 @@
   }
   delegate_->printMessage(std::string("CONSOLE ") + level + ": ");
   if (source_line) {
-    char buffer[40];
-    snprintf(buffer, sizeof(buffer), "line %d: ", source_line);
-    delegate_->printMessage(buffer);
+    delegate_->printMessage(base::StringPrintf("line %d: ", source_line));
   }
   if (!message.text.isEmpty()) {
     std::string new_message;