tree cb2bac3528f01cc8da4dfc927af0eb008da9afa4
parent 6804cef587bc27e870f085453b7174d817205af3
author Greg Spencer <gspencergoog@users.noreply.github.com> 1583946185 -0700
committer GitHub <noreply@github.com> 1583946185 -0700
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Convert Diagnosticable to a mixin (#51495)

This converts Diagnosticable to be a mixin instead of an abstract class, so that it can be used to add diagnostics to classes which already have a base class.

It leaves in place the DiagnosticableMixin mixin, since there are some plugins that are still using it, and removing it would mean that those plugins wouldn't work with master branch Flutter anymore. DiagnosticableMixin will be removed once this mixin version of Diagnosticable makes its way to the stable branch.