Fix definition of clearComposition to match the rest of the API

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 3344 matching lines @@
             ]
           }
         ]
       },
       {
         "name": "clearComposition",
         "type": "function",
         "description": "Clear the current composition. If this extension does not own the active IME, this fails.",
         "parameters": [
           {
-            "name": "contextID",
-            "description": "ID of the context with the composition text. This is the value provided in the InputContext from onFocus.",
-            "type": "integer"
+            "name": "parameters",
+            "type": "object",
+            "properties": {
+              "contextID": {
+                "description": "ID of the context where the composition will be cleared",
+                "type": "integer"
+              }
+            }
           },
           {
             "type": "function",
             "name": "callback",
             "optional": true,
             "description": "Called when the operation completes with a boolean indicating if the text was accepted or not. On failure, chrome.extension.lastError is set.",
             "parameters": [
               {
                 "name": "success",
                 "type": "boolean"
@@ skipping 5833 matching lines @@
                   }
                 }
               }
             ]
           }
         ]
       }
     ]
   }
 ]