Reland of Change extension icon load errors to warnings

extensions/test/data/file_util/bad_icon/manifest.json

Index: extensions/test/data/file_util/bad_icon/manifest.json
diff --git a/extensions/test/data/file_util/bad_icon/manifest.json b/extensions/test/data/file_util/bad_icon/manifest.json
index e3846e4cebf71d3f8e9c0369b1796f004f0981fd..27b7dac26fbb8968a7fffd77276e6c3742f42fd3 100644
--- a/extensions/test/data/file_util/bad_icon/manifest.json
+++ b/extensions/test/data/file_util/bad_icon/manifest.json
@@ -2,7 +2,9 @@
   "name": "My extension with a zero-length icon",
   "version": "1.0",
   "icons": {
-    "16": "icon.png"
+    "16": "good-icon.png",
+    "32": "missing-icon.png",
+    "64": "icon.png"
   },
   "manifest_version": 2
 }