ECHO asset swap: add reference to 32-px icon.

BUG=chromium-os:37884
TEST=manual verification

Review URL: https://codereview.chromium.org/12088088

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@180041 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/chromeos/echo/manifest.json

@@ -13,7 +13,8 @@
       "https://*/*"
    ],
   "icons": {
-    "16": "chrome16.png"
+    "16": "chrome16.png",
+    "32": "chrome32.png"
     },
   "default_locale": "en",
   "web_accessible_resources": [