Adding support to retrieve remaining and total space on disk/file shelf.

chrome/common/extensions/api/extension_api.json

 [
   {
     "namespace": "extension",
     "unprivileged": true,
     "types": [
       {
         "id": "MessageSender",
         "type": "object",
         "description": "An object containing information about the script context that sent a message or request.",
         "properties": {
@@ skipping 6737 matching lines @@
             "enum": ["device", "file", "network"],
             "description": "Type of the mount."
           },
           "mountCondition": {
             "type": "string",
             "description": "Additional data about mount, for example, that the filesystem is not supported."
           }
         }
       },
       {
+        "id": "MountPointSizeStats",
+        "type": "object",
+        "description": "Information about total and remaining size on the mount point.",
+        "properties": {
+          "totalSizeKB": {
+            "type": "integer",
+            "description": "Total available size on the mount point."
+          },
+          "remainingSizeKB": {
+            "type": "integer",
+            "description": "Remaining available size on the mount point."
+          }
+        }
+      },
+      {
         "id": "VolumeMetadata",
         "type": "object",
         "description": "Mounted disk volume metadata.",
         "properties": {
           "mountPath": {
             "type": "string",
             "description": "Disk volume mount point path."
           },
           "devicePath": {
             "type": "string",
@@ skipping 371 matching lines @@
                 "name" : "mountPoints",
                 "type": "array",
                 "items": {"$ref": "MountPointInfo"},
                 "description": "The list of MountPointInfo representing mounted devices."
               }
             ]
           }
         ]
       },
       {
+        "name": "getSizeStats",
+        "description": "Retrieves total and remaining size of a mount point.",
+        "parameters": [
+          {
+            "name": "mountPath",
+            "type": "string",
+            "description": "Mount point path."
+          },
+          {
+            "name": "callback",
+            "type": "function",
+            "optional": false,
+            "parameters": [
+              {
+                "name" : "sizeStats",
+                "$ref": "MountPointSizeStats",
+                "description": "Name/value pairs of size stats."
+              }
+            ]
+          }
+        ]
+      },
+      {
         "name": "formatDevice",
         "description": "Formats a mounted device",
         "parameters": [
           {
             "name": "mountPath",
             "type": "string",
             "description": "Device's mount path."
           }
         ]
       }
@@ skipping 1286 matching lines @@
             "type": "function",
             "description": "Called when the browser's passwords have been cleared.",
             "optional": true,
             "parameters": []
           }
         ]
       }
     ]
   }
 ]