Conflict detection for Extension Keybinding.

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

+{
+  "name": "Conflicting keybinding test, duplicate of Basics extension (dir next to this), but uses different colors",
+  "version": "1.0",
+  "manifest_version": 2,
+  "background": {
+    "scripts": ["background.js"]
+  },
+  "permissions": [
+    "tabs", "http://*/*", "experimental", "keybinding"
+  ],
+  "browser_action": {
+    "default_title": "Make this page green"
+  },
+  "commands": {
+    "toggle-feature": {
+      "suggested_key": {
+        "windows": "Ctrl+Shift+Y",
+        "mac": "Command+Shift+Y",
+        "linux": "Ctrl+Shift+Y",
+        "chromeos": "Ctrl+Shift+Y",
+        "default": "Ctrl+Shift+Y"
+      },
+      "description": "Toggle feature foo"
+    },
+    "_execute_browser_action": {
+      "suggested_key": {
+        "mac": "Command+Shift+F",
+        "default": "Ctrl+Shift+F"
+      }
+    }
+  }
+}