Continue key propagation for extensions without any listeners to chrome.commands.onCommand.

chrome/test/data/extensions/api_test/keybinding/continue_propagation/manifest.json

+{
+  "name": "An extension to test shortcuts propagation",
+  "version": "1.0",
+  "manifest_version": 2,
+  "background": {
+    "scripts": ["background.js"]
+  },
+  "permissions": [ "tabs" ],
+  "content_scripts": [
+    {
+      "matches": [ "<all_urls>" ],
+      "js": ["injected.js"]
+    }
+  ],
+  "commands": {
+    "Ctrl-Shift-F": {
+      "description": "Test propagation of this key",
+      "suggested_key": {
+        "default": "Ctrl+Shift+F",
+        "mac": "MacCtrl+Shift+F"
+      }
+    }
+  }
+}