Map double click keystroke

Bug: 854873
Change-Id: I511f782149470ce771c9f66802613e3bfbb7a4d8
Reviewed-on: https://chromium-review.googlesource.com/1115425Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570488}

chrome/browser/resources/chromeos/chromevox/chromevox/background/keymaps/next_keymap.json

@@ -940,6 +940,16 @@
           "keyCode": [65, 221]
         }
       }
+    },
+    {
+      "command": "forceClickOnCurrentItem",
+      "sequence": {
+        "cvoxModifier": true,
+        "keys": {
+          "keyCode": [32]
+        },
+        "doubleTap": true
+      }
     }
   ]
 }