Add 2 Extension APIs for handwriting: experimental.input.sendHandritingStroke and cancelHandWriting

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": {
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             },
             "description": "The keyboard event to be sent."
           },
           { "type": "function",
             "name": "callback",
             "optional": true,
             "description": "This function is called when the event processing is completed.",
             "parameters": []
           }
         ]
+      },
+      {
+        "name": "sendHandwritingStroke",
+        "type": "function",
+        "description": "Send a handwriting event to Chrome.",
+        "parameters": [
+          {
+            "name": "stroke",
+            "type": "array",
+            "items": {
+              "type": "object",
+              "properties": {
+                "x": {"type": "number", "minimum": 0, "maximum": 1},
+                "y": {"type": "number", "minimum": 0, "maximum": 1}
+              }
+            }
+          }
+        ]
+      },
+      {
+        "name": "cancelHandwriting",
+        "type": "function",
+        "description": "Clear last N handwriting strokes.",
+        "parameters": [
+          {
+            "name": "n_strokes",
+            "optional": true,
+            "type": "integer"
+          }
+        ]
       }
     ],
     "events": []
   },
   {
     "namespace": "experimental.bookmarkManager",
     "nodoc": true,
     "types": [
       {
         "id": "BookmarkNodeDataElement",
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           {
             "type": "integer",
             "name": "tabId",
             "description": "The id of the tab that was detached."
           }
         ]
       }
     ]
   }
 ]