Adding fullscreen mode access to chrome.fileBrowserPrivate API.

chrome/common/extensions/api/fileBrowserPrivate.json

 [
   {
     "namespace":"fileBrowserPrivate",
     "nodoc": "true",
     "types": [
       {
         "id": "FileBrowserTask",
         "type": "object",
         "description": "Represents information about available browser tasks. A task is an abstraction of an operation that the file browser can perform over a selected file set.",
         "properties": {
@@ skipping 512 matching lines @@
       {
         "name": "formatDevice",
         "description": "Formats a mounted device",
         "parameters": [
           {
             "name": "mountPath",
             "type": "string",
             "description": "Device's mount path."
           }
         ]
+      },
+      {
+        "name": "toggleFullscreen",
+        "description": "Switches fullscreen mode on/off for the File Browser.",
+        "parameters": []
+      },
+      {
+        "name": "isFullscreen",
+        "description": "Checks if the browser is in fullscreen mode.",
+        "parameters": [
+          {
+            "name": "callback",
+            "type": "function",
+            "optional": false,
+            "parameters": [
+              {
+                "name" : "result",
+                "type": "boolean",
+                "description": "Whether the browser is in fullscreen mode."
+              }
+            ]
+          }
+        ]
       }
     ],
     "events": [
       {
         "name": "onDiskChanged",
         "type": "function",
         "description": "Fired when disk mount/unmount event is detected.",
         "parameters": [
           {
             "$ref": "MountEvent",
@@ skipping 22 matching lines @@
           {
             "$ref": "FileWatchEvent",
             "name": "event",
             "description": "File watch event information."
           }
         ]
       }
     ]
   }
 ]