Add extensions test data for an empty icon image

Part of extensions refactoring in https://codereview.chromium.org/562273006/

Landing manually because the tryjob patch step cannot handle empty binary files

BUG=none
TEST=none
TBR=yoz@chromium.org

Review URL: https://codereview.chromium.org/580283003

Cr-Commit-Position: refs/heads/master@{#295556}

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

+{
+  "name": "My extension with a zero-length icon",
+  "version": "1.0",
+  "icons": {
+    "16": "icon.png"
+  },
+  "manifest_version": 2
+}