Simplify ExtensionInstallChecker into a single-use class

chrome/browser/extensions/extension_browsertest.h

 // Copyright (c) 2012 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 CHROME_BROWSER_EXTENSIONS_EXTENSION_BROWSERTEST_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_BROWSERTEST_H_
 
 #include <string>
 
 #include "base/command_line.h"
@@ skipping 245 matching lines @@
   bool WaitForExtensionLoadError() {
     return observer_->WaitForExtensionLoadError();
   }
 
   // Wait for the specified extension to crash. Returns true if it really
   // crashed.
   bool WaitForExtensionCrash(const std::string& extension_id) {
     return observer_->WaitForExtensionCrash(extension_id);
   }
 
-  // Wait for the crx installer to be done. Returns true if it really is done.
+  // Wait for the crx installer to be done. Returns true if it has finished
+  // successfully.
   bool WaitForCrxInstallerDone() {
     return observer_->WaitForCrxInstallerDone();
   }
 
   // Wait for all extension views to load.
   bool WaitForExtensionViewsToLoad() {
     return observer_->WaitForExtensionViewsToLoad();
   }
 
   // Wait for the extension to be idle.
@@ skipping 117 matching lines @@
   std::unique_ptr<extensions::ExtensionCacheFake> test_extension_cache_;
 
   // An override so that chrome-extensions://<extension_id>/_test_resources/foo
   // maps to chrome/test/data/extensions/foo.
   extensions::ExtensionProtocolTestHandler test_protocol_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionBrowserTest);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_BROWSERTEST_H_