Simplify ExtensionInstallChecker into a single-use class

chrome/browser/extensions/crx_installer_browsertest.cc

Index: chrome/browser/extensions/crx_installer_browsertest.cc
diff --git a/chrome/browser/extensions/crx_installer_browsertest.cc b/chrome/browser/extensions/crx_installer_browsertest.cc
index 36098b82f44caf7686064726b18bea1e18e82006..d2af79003905c472d3ebe13b3e72de6c0aeb72b3 100644
--- a/chrome/browser/extensions/crx_installer_browsertest.cc
+++ b/chrome/browser/extensions/crx_installer_browsertest.cc
@@ -284,16 +284,7 @@ class ExtensionCrxInstallerTest : public ExtensionBrowserTest {
         CreateWebAppInfo(kAppTitle, kAppDescription, kAppUrl, 64));
     EXPECT_TRUE(WaitForCrxInstallerDone());
     ASSERT_TRUE(crx_installer->extension());
-    ASSERT_FALSE(HasRequirementErrors(crx_installer.get()));
-    ASSERT_FALSE(HasPolicyErrors(crx_installer.get()));
-  }
-
-  bool HasRequirementErrors(CrxInstaller* crx_installer) {
-    return !crx_installer->install_checker_.requirement_errors().empty();
-  }
-
-  bool HasPolicyErrors(CrxInstaller* crx_installer) {
-    return !crx_installer->install_checker_.policy_error().empty();
+    ASSERT_EQ(nullptr, crx_installer->install_checker_.get());

[Devlin, 2017/03/16 19:29:40]

This is testing an implementation detail of the CrxInstaller, rather than
behavior.  If we ever decide to instantiate install_checker_ when there are no
errors, this will fail.  Additionally, this wouldn't catch the case of an
installation being triggered, the install checker running, and finding no
errors.

[michaelpg, 2017/03/17 04:25:22]

This turns out to be the only user of WaitForCrxInstallerDone(), so I've
modified that to ensure the installer finishes *successfully*. So I feel OK
removing this check, which also lets us unfriend CrxInstaller!

   }
 };