Whitelist QuickOffice extension to use the mimeHandler private API.

Bug: 819761
Change-Id: I7d34886e5d12b1a77287463a6d15daf054192858
Reviewed-on: https://chromium-review.googlesource.com/956965Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542262}

extensions/common/api/_manifest_features.json

@@ -231,6 +231,7 @@
     "extension_types": [ "extension", "legacy_packaged_app", "platform_app" ],
     "whitelist": [
       "787000072C6FBB934AF5A42275CDE73FC977D995",  // browser_tests
+      "2FC374607C2DF285634B67C64A2E356C607091C3",  // QuickOffice
       "CBCC42ABED43A4B58FE3810E62AFFA010EB0349F"   // PDF
     ]
   },