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- The WebstoreStandaloneInstaller now supports error codes to allow
translation to API error codes.
- The EphemeralAppLauncher now also returns error codes and performs
more checks before installing an ephemeral app or enabling an
installed app.
- Introduces the ExtensionInstallChecker, which checks blacklist
state, requirement errors and management policies for a given
extension.

BUG=380980
TEST=browser_tests (EphemeralAppLauncherTest.*)
unit_tests (ExtensionInstallCheckerTest.*)

Review URL: https://codereview.chromium.org/339103002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278890 0039d316-1c4b-4281-b951-d872f2087c98