Spelling correction: "nonexistant" -> "nonexistent".

BUG=none
TEST=good spellers are slightly happier

Review URL: http://codereview.chromium.org/3143037

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@57020 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/extensions/extensions_service.cc b/chrome/browser/extensions/extensions_service.cc
index 58ead19..e055f614 100644
--- a/chrome/browser/extensions/extensions_service.cc
+++ b/chrome/browser/extensions/extensions_service.cc
@@ -406,7 +406,7 @@
                                            bool external_uninstall) {
   Extension* extension = GetExtensionByIdInternal(extension_id, true, true);
 
-  // Callers should not send us nonexistant extensions.
+  // Callers should not send us nonexistent extensions.
   DCHECK(extension);
 
   // Notify interested parties that we're uninstalling this extension.
@@ -901,7 +901,7 @@
   scoped_ptr<Extension> extension(
       GetExtensionByIdInternal(extension_id, true, true));
 
-  // Callers should not send us nonexistant extensions.
+  // Callers should not send us nonexistent extensions.
   CHECK(extension.get());
 
   // Keep information about the extension so that we can reload it later