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..802f2a9175bc0b71d67d60fc9756736585e5f98e 100644
--- a/chrome/browser/extensions/crx_installer.h
+++ b/chrome/browser/extensions/crx_installer.h
@@ -12,6 +12,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/version.h"
+#include "chrome/browser/extensions/app_host_installer.h"
 #include "chrome/browser/extensions/crx_installer_error.h"
 #include "chrome/browser/extensions/extension_install_prompt.h"
 #include "chrome/browser/extensions/sandboxed_unpacker.h"
@@ -31,7 +32,7 @@ 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 +215,17 @@ 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 +316,7 @@ 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_;
 
@@ -359,6 +369,9 @@ class CrxInstaller
 
   bool has_requirement_errors_;
 
+  // Helper to install App Host.
+  AppHostInstaller app_host_installer_;
+
   DISALLOW_COPY_AND_ASSIGN(CrxInstaller);
 };