Simplify ExtensionInstallChecker into a single-use class

chrome/browser/extensions/extension_browsertest.h

Index: chrome/browser/extensions/extension_browsertest.h
diff --git a/chrome/browser/extensions/extension_browsertest.h b/chrome/browser/extensions/extension_browsertest.h
index 55eecc6c657f2b5cec2930e5376bd1324800c9c4..ca8782035a7b5d54a4a33a439f26fda2e94ac1d1 100644
--- a/chrome/browser/extensions/extension_browsertest.h
+++ b/chrome/browser/extensions/extension_browsertest.h
@@ -263,7 +263,8 @@ class ExtensionBrowserTest : virtual public InProcessBrowserTest {
     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();
   }