[headless] Make browser service manifest overlay configurable.

headless/test/headless_browser_test.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef HEADLESS_TEST_HEADLESS_BROWSER_TEST_H_
 #define HEADLESS_TEST_HEADLESS_BROWSER_TEST_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 62 matching lines @@
 
   // Synchronously evaluates a script and returns the result.
   std::unique_ptr<runtime::EvaluateResult> EvaluateScript(
       HeadlessWebContents* web_contents,
       const std::string& script);
 
  protected:
   // Returns the browser for the test.
   HeadlessBrowser* browser() const;
 
+  // Returns the options used by the browser. Modify with caution, since some
+  // options only take effect if they were set before browser creation.
+  HeadlessBrowser::Options* options() const;
+
  private:
   std::unique_ptr<base::RunLoop> run_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(HeadlessBrowserTest);
 };
 
 #define HEADLESS_ASYNC_DEVTOOLED_TEST_F(TEST_FIXTURE_NAME)               \
   IN_PROC_BROWSER_TEST_F(TEST_FIXTURE_NAME, RunAsyncTest) { RunTest(); } \
   class AsyncHeadlessBrowserTestNeedsSemicolon##TEST_FIXTURE_NAME {}
 
@@ skipping 18 matching lines @@
   void RunTest();
 
   HeadlessBrowserContext* browser_context_;  // Not owned.
   HeadlessWebContents* web_contents_;
   std::unique_ptr<HeadlessDevToolsClient> devtools_client_;
 };
 
 }  // namespace headless
 
 #endif  // HEADLESS_TEST_HEADLESS_BROWSER_TEST_H_