Add the "file_handlers" manifest key for platform apps to replace "intents".

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 b3b9ecaec5245f111822711bfcfbdc87bd9eec84..18e629a00994644168e5a936b575619d28dc92a5 100644
--- a/chrome/common/extensions/extension_manifest_constants.h
+++ b/chrome/common/extensions/extension_manifest_constants.h
@@ -38,6 +38,9 @@ namespace extension_manifest_keys {
   extern const char kExcludeGlobs[];
   extern const char kExcludeMatches[];
   extern const char kFileAccessList[];
+  extern const char kFileHandlers[];
+  extern const char kFileHandlerTitle[];
+  extern const char kFileHandlerTypes[];
   extern const char kFileFilters[];
   extern const char kFileBrowserHandlers[];
   extern const char kHomepageURL[];
@@ -207,6 +210,10 @@ namespace extension_manifest_errors {
   extern const char kInvalidFileBrowserHandler[];
   extern const char kInvalidFileFiltersList[];
   extern const char kInvalidFileFilterValue[];
+  extern const char kInvalidFileHandlers[];
+  extern const char kInvalidFileHandlerTitle[];
+  extern const char kInvalidFileHandlerType[];
+  extern const char kInvalidFileHandlerTypeElement[];
   extern const char kInvalidGlob[];
   extern const char kInvalidGlobList[];
   extern const char kInvalidHomepageURL[];