override chrome:// URLs via extensions.

chrome/common/extensions/extension_constants.cc

Index: chrome/common/extensions/extension_constants.cc
diff --git a/chrome/common/extensions/extension_constants.cc b/chrome/common/extensions/extension_constants.cc
index d887678c2d619ed00d8ec2ad46c60c815221219d..d72fbcf0dddce1c68dc19bb3f704833e32db1f65 100644
--- a/chrome/common/extensions/extension_constants.cc
+++ b/chrome/common/extensions/extension_constants.cc
@@ -7,6 +7,7 @@
 namespace extension_manifest_keys {
 
 const wchar_t* kBackground = L"background_page";
+const wchar_t* kChromeURLOverrides = L"chrome_url_overrides";
 const wchar_t* kContentScripts = L"content_scripts";
 const wchar_t* kCss = L"css";
 const wchar_t* kDefaultLocale = L"default_locale";
@@ -52,6 +53,8 @@ const char* kPageActionTypePermanent = "permanent";
 // printf because we want to unit test them and scanf is hard to make
 // cross-platform.
 namespace extension_manifest_errors {
+const char* kInvalidChromeURLOverrides =
+    "Invalid value for 'chrome_url_overrides'.";
 const char* kInvalidContentScript =
     "Invalid value for 'content_scripts[*]'.";
 const char* kInvalidContentScriptsList =