Change the platform app manifest structure.

chrome/common/extensions/extension_manifest_constants.h

Index: chrome/common/extensions/extension_manifest_constants.h
diff --git a/chrome/common/extensions/extension_manifest_constants.h b/chrome/common/extensions/extension_manifest_constants.h
index bb285f4a64465a3ac9e0c359dc50af27fb9471a0..88531d94b3c097c1a2c6320286982ef265dcdb96 100644
--- a/chrome/common/extensions/extension_manifest_constants.h
+++ b/chrome/common/extensions/extension_manifest_constants.h
@@ -93,7 +93,9 @@ namespace extension_manifest_keys {
   extern const char kPageActionPopupPath[];
   extern const char kPageActions[];
   extern const char kPermissions[];
-  extern const char kPlatformApp[];
+  extern const char kPlatformAppBackground[];
+  extern const char kPlatformAppBackgroundPage[];
+  extern const char kPlatformAppBackgroundScripts[];
   extern const char kPlugins[];
   extern const char kPluginsPath[];
   extern const char kPluginsPublic[];
@@ -315,6 +317,8 @@ namespace extension_manifest_errors {
   extern const char kNoWildCardsInPaths[];
   extern const char kPermissionNotAllowed[];
   extern const char kPlatformAppFlagRequired[];
+  extern const char kPlatformAppInvalidBackgroundPage[];
+  extern const char kPlatformAppInvalidBackgroundScripts[];
   extern const char kPlatformAppNeedsManifestVersion2[];
   extern const char kOneUISurfaceOnly[];
   extern const char kReservedMessageFound[];