Most annoyingly the text in comment boxes would sometimes shift to the
left. The reason for that was that box-sizing:border-box was not applied
correctly. Investigating this I realized that multiple
--iron-autogrow-textarea specs would not be merged, so often the
padding-only in shared-styles would win.
--iron-autogrow-textarea without a colon was not working at all.
Consolidated --iron-autogrow-textarea in shared-styles and
gr-editable-content.
Change-Id: Iab6171d4d05069840b36e3d8c9f95a47f23d8a3e
0773d83413