Implement gallery install 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 3987 matching lines @@
           },
           {
             "name": "callback",
             "type": "function",
             "optional": "true",
             "parameters": []
           }
         ]
       },
       {
-        "name": "install",
-        "description": "(FOR INTERNAL USE ONLY)",
-        "nodoc": true,
-        "parameters": [
-          {
-            "name": "expected_id",
-            "type": "string",
-            "description": "The id we expect the crx at |url| to have."
-          },
-          {
-            "name": "url",
-            "type": "string",
-            "description": "The url to fetch the crx from."
-          },
-          {
-            "name": "callback",
-            "type": "function",
-            "optional": "true",
-            "parameters": []
-          }
-        ]
-      },
-      {
         "name": "uninstall",
         "description": "Uninstall a currently installed app or extension.",
         "parameters": [
           {
             "name": "id",
             "type": "string",
             "description": "This should be the id from an item of $ref:ExtensionInfo."
           },
           {
             "name": "callback",
@@ skipping 30 matching lines @@
         "parameters": [{"name": "info", "$ref":"ExtensionInfo"}]
       }
     ]
   },
 
   {
     "namespace":"webstorePrivate",
     "nodoc": "true",
     "functions": [
       {
+        "name": "install",
+        "description": "Installs the extension corresponding to the given id",
+        "parameters": [
+          {
+            "name": "expected_id",
+            "type": "string",
+            "description": "The id of the extension to install."
+          },
+          {
+            "name": "callback",
+            "type": "function",
+            "optional": "true",
+            "parameters": []
+          }
+        ]
+      },
+      {
         "name": "getSyncLogin",
         "description": "Returns the logged-in sync user login if there is one, or the empty string otherwise.",
         "parameters": [
           {
             "name": "callback",
             "type": "function",
             "optional": "false",
             "parameters": [
               { "name": "login", "type": "string" }
             ]
@@ skipping 18 matching lines @@
         "name": "setStoreLogin",
         "description": "Set a preference value with the store login.",
         "parameters": [
           { "name": "login", "type": "string" },
           { "name": "callback", "type": "function", "optional": "true" }
         ]
       }
     ]
   }
 ]