Adds a webstorePrivate method for silently installing extensions.

chrome/common/extensions/api/extension_api.json

Index: chrome/common/extensions/api/extension_api.json
diff --git a/chrome/common/extensions/api/extension_api.json b/chrome/common/extensions/api/extension_api.json
index 7e25c336370109731651fa5c72c712081faf4164..1230a7495a415615774a8092db121c1a1b999314 100644
--- a/chrome/common/extensions/api/extension_api.json
+++ b/chrome/common/extensions/api/extension_api.json
@@ -7904,7 +7904,7 @@
           {
             "name": "expected_id",
             "type": "string",
-            "description": "The id of the extension to be installled. This should match a previous call to beginInstallWithManifest3."
+            "description": "The id of the extension to be installed. This should match a previous call to beginInstallWithManifest3."
           },
           {
             "name": "callback",
@@ -7915,6 +7915,42 @@
         ]
       },
       {
+        "name": "silentlyInstall",
+        "description": "Silently installs the specified extension, which must already be whitelisted in Chrome.",
+        "parameters": [
+          {
+            "name": "details",
+            "type": "object",
+            "properties": {
+              "id": {
+                "type": "string",
+                "description": "The id of the extension to be installled.",
+                "minLength": 32,
+                "maxLength": 32
+              },
+              "manifest": {
+                "type": "string",
+                "description": "A string with the contents of the extension's manifest.json file. During the install process, the browser will check that the downloaded extension's manifest matches what was passed in here.",
+                "minLength": 1
+              }
+            }
+          },
+          {
+            "name": "callback",
+            "type": "function",
+            "description": "Called when the user has either accepted/rejected the dialog, or some error occurred (such as invalid manifest or icon image data).",
+            "optional": "true",
+            "parameters": [
+              {
+                "name": "result",
+                "type": "string",
+                "description": "A string result code, which will be empty upon success. The possible values in the case of errors include 'unknown_error', 'manifest_error', 'invalid_id' and  'permission_denied'."
+              }
+            ]
+          }
+        ]
+      },
+      {
         "name": "getBrowserLogin",
         "description": "Returns the logged-in sync user login if there is one, or the empty string otherwise.",
         "parameters": [