Updating JSON Schema Compiler to add description field to schemas.

tools/json_schema_compiler/test/tabs.json

 [
   {
     "namespace": "tabs",
+    "description": "The tabs API.",
     "types": [
       {
         "id": "Tab",
         "type": "object",
         "properties": {
           "id": {"type": "integer", "minimum": 0, "description": "The ID of the tab. Tab IDs are unique within a browser session."},
           "index": {"type": "integer", "minimum": 0, "description": "The zero-based index of the tab within its window."},
           "windowId": {"type": "integer", "minimum": 0, "description": "The ID of the window the tab is contained within."},
           "selected": {"type": "boolean", "description": "Whether the tab is selected.", "nodoc": true},
           "highlighted": {"type": "boolean", "description": "Whether the tab is highlighted."},
@@ skipping 746 matching lines @@
             "name": "removeInfo",
             "properties": {
               "isWindowClosing": {"type": "boolean", "description": "True when the tab is being closed because its window is being closed." }
             }
           }
         ]
       }
     ]
   }
 ]