Do IWYU for base/strings/stringprintf.h in chrome/.

It currently works because ipc/ipc_message_utils.h is included in many
places transitively, and it unnecessarily includes
base/strings/stringprintf.h.

Change-Id: I8d1a17805e23eb78b4c833798eedb00312c2ed7a
Reviewed-on: https://chromium-review.googlesource.com/c/1449159
Reviewed-by: Sergey Poromov <[email protected]>
Commit-Queue: Lei Zhang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#628369}
diff --git a/chrome/browser/extensions/app_process_apitest.cc b/chrome/browser/extensions/app_process_apitest.cc
index 6579e8e2..fd1b73d 100644
--- a/chrome/browser/extensions/app_process_apitest.cc
+++ b/chrome/browser/extensions/app_process_apitest.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "base/command_line.h"
+#include "base/strings/stringprintf.h"
 #include "build/build_config.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/extensions/extension_apitest.h"