Add support for persistent file access in apps.

chrome/common/extensions/api/_permission_features.json

Index: chrome/common/extensions/api/_permission_features.json
diff --git a/chrome/common/extensions/api/_permission_features.json b/chrome/common/extensions/api/_permission_features.json
index 0c21648f1826c56e4c12c2630d01e7f914c5f721..d5d1f3178feb3f09ddd40393d99e01a854093e4c 100644
--- a/chrome/common/extensions/api/_permission_features.json
+++ b/chrome/common/extensions/api/_permission_features.json
@@ -208,6 +208,14 @@
     "extension_types": ["extension"],
     "whitelist": [ "2FC374607C2DF285634B67C64A2E356C607091C3" ]
   }],
+  "fileSystem.retainFiles": [{
+    "channel": "stable",

[benwells, 2013/05/16 06:50:17]

Let's restrict this to trunk until we get the UI done as well.

[Sam McNally, 2013/05/17 03:38:52]

Done.

+    "extension_types": ["platform_app"]
+  },{
+    "channel": "stable",

[benwells, 2013/05/16 06:50:17]

Also let's not give this to QuickOffice unless they need it (i.e. let's not
perpetuate this hack ...)

[Sam McNally, 2013/05/17 03:38:52]

Done.

+    "extension_types": ["extension"],
+    "whitelist": [ "2FC374607C2DF285634B67C64A2E356C607091C3" ]
+  }],
   "fileSystem.write": [{
     "channel": "stable",
     "extension_types": ["platform_app"]