Replace ExtensionInstallChecker with generic PreloadCheckGroup

extensions/browser/requirements_checker_unittest.cc

Index: extensions/browser/requirements_checker_unittest.cc
diff --git a/extensions/browser/requirements_checker_unittest.cc b/extensions/browser/requirements_checker_unittest.cc
index c4532f74b89b3738f8b30efc27b31a0e4fbcd345..6890c918cc2922dba075b0229dca4070ee471b42 100644
--- a/extensions/browser/requirements_checker_unittest.cc
+++ b/extensions/browser/requirements_checker_unittest.cc
@@ -165,7 +165,6 @@ TEST_F(RequirementsCheckerTest, RequirementsFailWebGL) {
 
   // TODO(michaelpg): Check that the runner actually finishes, which requires
   // waiting for the GPU check to succeed: crbug.com/706204.
-  runner_.WaitForIdle();
   if (runner_.errors().size()) {
     EXPECT_THAT(runner_.errors(), testing::UnorderedElementsAre(
                                       PreloadCheck::WEBGL_NOT_SUPPORTED));