Add visual snapshots for icon buttons (#1501)

Author: jhardy

CHANGELOG.md

@@ -14,7 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Preview: `ActionListControls` component (this component is not yet ready for general-use)
 * Experimental: `@looker/components-theme-editor` package
 * Experimental: "Semantic" Layout components - `Layout`, `Header`, `Footer`, `Aside`
-- Implemented image snapshot support and added coverage for `Button*` components
+- Implemented image snapshot support and added coverage for `Button*`, `IconButton` components
 - Preliminary infrastructure for Storybook composition
 - Added support for Storybook extract behavior to improve published-Storybook performance
 
@@ -25,6 +25,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - `addons-essentials` now used
   - Replace `withKnobs` with `Controls` & `Args`
 
+
+
 ## [0.9.15] - 2020-09-21
 
 ### Changed