Fix an issue where clicking the search icon would submit the form

Clicking the search icon should only focus the search field,
not submit the search.

This addresses the issue mentioned at https://github.com/hypothesis/h/pull/2622#issuecomment-148808509

h/static/scripts/directive/simple-search.coffee

@@ -41,10 +41,10 @@ module.exports = ['$http', '$parse', ($http, $parse) ->
                      placeholder="{{loading && 'Loading' || 'Search'}}…"
                      ng-disabled="loading"
                      ng-class="(alwaysExpanded || searchtext.length > 0) ? 'is-expanded' : ''"/>
-              <button class="simple-search-icon top-bar__btn" ng-hide="loading">
+              <button type="button" class="simple-search-icon top-bar__btn" ng-hide="loading">
                 <i class="h-icon-search"></i>
               </button>
-              <button class="simple-search-icon btn btn-clean" ng-show="loading" disabled>
+              <button type="button" class="simple-search-icon btn btn-clean" ng-show="loading" disabled>
                 <span class="btn-icon"><span class="spinner"></span></span>
               </button>
             </form>

h/static/scripts/directive/test/simple-search-test.coffee

@@ -35,9 +35,17 @@ describe 'simple-search', ->
     '''
 
     $element = $compile(angular.element(template))($scope)
+
+    # add element to document so that it becomes focusable
+    # and we get default form behaviors
+    document.body.appendChild($element[0])
+
     $scope.$digest()
     isolate = $element.isolateScope()
 
+  afterEach ->
+    document.body.removeChild($element[0])
+
   it 'updates the search-bar', ->
     $scope.query = "Test query"
     $scope.$digest()
@@ -75,3 +83,26 @@ describe 'simple-search', ->
     fakeHttp.pendingRequests = ['bogus']
     isolate.$digest()
     assert.isTrue(isolate.loading)
+
+  it 'expands the search field when the input is non-empty', ->
+    input = $element.find('.simple-search-input')
+    assert.isFalse(input.hasClass('is-expanded'))
+    input.val('query')
+    input.trigger('change')
+    isolate.$digest()
+    assert.isTrue(input.hasClass('is-expanded'))
+
+  it 'focuses the search field when clicking the search button', ->
+    input = $element.find('.simple-search-input')
+    searchBtn = $element.find('button')
+    assert.ok(document.activeElement != input[0])
+    searchBtn.click()
+    assert.ok(document.activeElement == input[0])
+
+  it 'does not update the search when clicking the search button', ->
+    searchBtn = $element.find('button')
+    input = $element.find('.simple-search-input')
+    input.val('query')
+    input.trigger('change')
+    searchBtn.click()
+    assert.notCalled($scope.update)