Adding support for mount point different from removable devices to MountLibrary

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 5226 matching lines @@
             "enum": ["added", "removed"],
             "description": "Event type that tells listeners which disk volume even was raised."
           },
           "volumeInfo": {
             "$ref": "VolumeInfo",
             "description":"Volume information that this mount event applies to."
           }
         }
       },
       {
+        "id": "MountCompletedEvent",
+        "type": "object",
+        "description": "Payload data for mount event.",
+        "properties": {
+          "eventType": {
+            "type": "string",
+            "enum": ["success", "auth_required", "bad_password",
+                     "network_error", "libcros_missing", "internal", "unknown"],
+            "description": "Event type that tells listeners if mount was successfull or an error occurred. It also specifies the error."
+          },
+          "sourcePath": {
+            "type": "string",
+            "description":"Path that has been mounted."
+          },
+          "mountPath": {
+            "type": "string",
+            "description":"Path that sourcePath was mounted to."
+          },
+          "mountType": {
+            "type": "string",
+            "enum": ["device", "file"],
+            "description":"Type of the mount."
+          }
+        }
+      },
+      {
         "id": "FileWatchEvent",
         "type": "object",
         "description": "Payload data for disk mount / unmount event.",
         "properties": {
           "eventType": {
             "type": "string",
             "enum": ["changed", "error"],
             "description": "Specifies type of event that is raised."
           },
           "fileUrl": {
@@ skipping 238 matching lines @@
         "description": "Fired when disk mount/unmount event is detected.",
         "parameters": [
           {
             "$ref": "MountEvent",
             "name": "event",
             "description": "Mount event information."
           }
         ]
       },
       {
+        "name": "onMountCompleted",
+        "type": "function",
+        "description": "Fired when mount event is detected.",
+        "parameters": [
+          {
+            "$ref": "MountCompletedEvent",
+            "name": "event",
+            "description": "MountCompleted event information."
+          }
+        ]
+      },
+      {
         "name": "onFileChanged",
         "type": "function",
         "description": "Fired when watched file change event is detected.",
         "parameters": [
           {
             "$ref": "FileWatchEvent",
             "name": "event",
             "description": "File watch event information."
           }
         ]
@@ skipping 1026 matching lines @@
                 "description": "A string result code. The value is non-empty on success only in tests.",
                 "optional": "true"
               }
             ]
           }
         ]
       }
     ]
   }
 ]