Make application shortcuts point to app_host.exe, install App Host during app installation.

chrome/browser/extensions/crx_installer.h

Index: chrome/browser/extensions/crx_installer.h
diff --git a/chrome/browser/extensions/crx_installer.h b/chrome/browser/extensions/crx_installer.h
index e9541dec8204defc135dbc6dfef30595eab22ef2..5cc2140f8d1ea3931c89b50f9a8b1f2b85e975d5 100644
--- a/chrome/browser/extensions/crx_installer.h
+++ b/chrome/browser/extensions/crx_installer.h
@@ -31,7 +31,7 @@ class RequirementsChecker;
 //
 // Installing a CRX is a multi-step process, including unpacking the crx,
 // validating it, prompting the user, and installing. Since many of these
-// steps must occur on the file thread, this class contains a copy of all data
+// steps must occur on the FILE thread, this class contains a copy of all data
 // necessary to do its job. (This also minimizes external dependencies for
 // easier testing).
 //
@@ -214,8 +214,17 @@ class CrxInstaller
   // that it is OK to install this extension.
   void ConfirmInstall();
 
-  // Runs on File thread. Install the unpacked extension into the profile and
-  // notify the frontend.
+  // Runs on FILE thread. Ensures that app is not downgraded. If App Host is
+  // not installed, calls installer and posts OnAppHostInstallationComplete()
+  // as call back.  Else proceeds to CompleteInstall().
+  void BeginInstall();
+
+  // Runs on FILE thread. Callback function for AppHostInstaller.
+  // If not |success|, shows error message. Else proceeds to CompleteInstall().
+  void OnAppHostInstallationComplete(bool success);
+
+  // Runs on FILE thread. Installs the unpacked extension into the profile and
+  // notifies the frontend.
   void CompleteInstall();
 
   // Result reporting.
@@ -306,7 +315,7 @@ class CrxInstaller
 
   // The client we will work with to do the installation. This can be NULL, in
   // which case the install is silent.
-  // NOTE: we may be deleted on the file thread. To ensure the UI is deleted on
+  // NOTE: we may be deleted on the FILE thread. To ensure the UI is deleted on
   // the main thread we don't use a scoped_ptr here.
   ExtensionInstallPrompt* client_;