Move IPC fuzzer switches and helpers from chrome/common to content/common.

content/content_common.gypi

Index: content/content_common.gypi
diff --git a/content/content_common.gypi b/content/content_common.gypi
index 3c4be3437bc0f3309a723bfb9f9fa9850a50721c..a44d135dd52418ec3edf73edca32d1b014e5020c 100644
--- a/content/content_common.gypi
+++ b/content/content_common.gypi
@@ -660,5 +660,11 @@
         'common/gpu/gpu_memory_buffer_factory_ozone_native_pixmap.h',
       ],
     }],
+    ['enable_ipc_fuzzer==1', {
+      'sources': [
+        'public/common/external_ipc_dumper.cc',
+        'public/common/external_ipc_dumper.h',
+      ],
+    }],
   ],
 }