Extension-created windows should share the creator's BrowingInstance.

chrome/browser/extensions/extension_apitest.h

Index: chrome/browser/extensions/extension_apitest.h
diff --git a/chrome/browser/extensions/extension_apitest.h b/chrome/browser/extensions/extension_apitest.h
index 7b1a1936ebd602b65a353af6f25a21b0c42c7e8b..541536520cc6ae0b5764399474ead87ee7452886 100644
--- a/chrome/browser/extensions/extension_apitest.h
+++ b/chrome/browser/extensions/extension_apitest.h
@@ -72,6 +72,11 @@ class ExtensionApiTest : public ExtensionBrowserTest {
   // |extension_name| is a directory in "test/data/extensions/api_test".
   bool RunExtensionTest(const std::string& extension_name);
 
+  // Similar to RunExtensionTest, except sets an additional string argument
+  // |customArg| to the test config object.
+  bool RunExtensionTestWithArg(const std::string& extension_name,
+                               const char* custom_arg);
+
   // Same as RunExtensionTest, but enables the extension for incognito mode.
   bool RunExtensionTestIncognito(const std::string& extension_name);