The <content> element is deprecated, part of the Shadow DOM v0 API
which has been supplanted by Shadow DOM v1's <slot> element. For very
simple uses – like those in this change – this change should be safe
and will not require changes to the usage sites of your element.
Therefore, these changes are backwards-compatible with Polymer 1.0
applications.
As <content> is the more powerful API, Polymer 1.0 supports both
<content> and <slot> by converting <slot> back into <content> at
runtime. Polymer 2.0 only supports <slot>. There will likely never be
cross-browser native support for <content>, while Safari and Chrome
already support <slot> natively.
PiperOrigin-RevId: 174107440
Change-Id: I21fd97ff6efe95231089f98853146353e0e4ebf2
d78b793cf7