I was looking for an example of extensible search in Angular with Material, too, and found this code in Codepen, but I'm not sure if it is exactly what you are looking for, it opens full-size input using the back button ...
http://codepen.io/kyleledbetter/pen/gbQOaV
The HTML toolbar looks something like this:
<md-toolbar ng-show="!showSearch"> <div class="md-toolbar-tools"> <md-button ng-click="toggleSidenav('left')" hide-gt-md aria-label="Menu"> <ng-md-icon icon="menu"></ng-md-icon> </md-button> <h3> Dashboard </h3> <span flex></span> <md-button aria-label="Search" ng-click="showSearch = !showSearch"> <ng-md-icon icon="search"></ng-md-icon> </md-button> <md-button aria-label="Open Settings" ng-click="showListBottomSheet($event)"> <ng-md-icon icon="more_vert"></ng-md-icon> </md-button> </div> </md-toolbar> <md-toolbar class="md-hue-1" ng-show="showSearch"> <div class="md-toolbar-tools"> <md-button ng-click="showSearch = !showSearch" aria-label="Back"> <ng-md-icon icon="arrow_back"></ng-md-icon> </md-button> <h3 flex="10"> Back </h3> <md-input-container md-theme="input" flex> <label> </label> <input ng-model="search.who" placeholder="enter search"> </md-input-container> <md-button aria-label="Search" ng-click="showSearch = !showSearch"> <ng-md-icon icon="search"></ng-md-icon> </md-button> <md-button aria-label="Open Settings" ng-click="showListBottomSheet($event)"> <ng-md-icon icon="more_vert"></ng-md-icon> </md-button> </div> </md-toolbar>
Dunos source share