Use an icon to set the email instead of a button with string

apps/files_sharing/css/sharetabview.css

 	margin-left: 0;
 }
 .shareTabView input[type="text"].shareWithField,
+.shareTabView input[type="text"].emailField,
 .shareTabView input[type="text"].linkText {
 	width: 80%;
 }

core/css/icons.css

 	background-image: url('../img/actions/mail.svg');
 }
 
+.icon-mail-grey {
+	background-image: url('../img/actions/mail-grey.svg');
+}
+
 .icon-menu {
 	background-image: url('../img/actions/menu.svg');
 }

core/js/sharedialogmailview.js

 	var TEMPLATE = 
 			'{{#if shareAllowed}}' +
 			'    {{#if mailPublicNotificationEnabled}}' +
-			'<form id="emailPrivateLink" class="emailPrivateLinkForm">' +
+			'<form id="emailPrivateLink" class="emailPrivateLinkForm oneline">' +
 			'    <input id="email" class="emailField" value="{{email}}" placeholder="{{mailPrivatePlaceholder}}" type="text" />' +
-			'    <input id="emailButton" class="emailButton" type="submit" value="{{mailButtonText}}" />' +
+			'    <a id="emailButton" class="icon icon-mail-grey" />' +
 			'</form>' +
 			'    {{/if}}' +
 			'{{/if}}'
 		showLink: true,
 
 		events: {
-			'submit .emailPrivateLinkForm': '_onEmailPrivateLink'
+			'click #emailButton': '_onEmailPrivateLink'
 		},
 
 		initialize: function(options) {
 
 	OC.Share.ShareDialogMailView = ShareDialogMailView;
 
-})();
+})();

core/js/tests/specs/sharedialogviewSpec.js

 				dialog.render();
 
 				dialog.$el.find('.emailPrivateLinkForm .emailField').val('a@b.c');
-				dialog.$el.find('.emailPrivateLinkForm').trigger('submit');
+				dialog.$el.find('#emailButton').trigger('click');
 
 				expect(sendEmailPrivateLinkStub.callCount).toEqual(1);
 				expect(dialog.$el.find('.emailPrivateLinkForm .emailField').val()).toEqual('Sending ...');
 				dialog.render();
 
 				dialog.$el.find('.emailPrivateLinkForm .emailField').val('a@b.c');
-				dialog.$el.find('.emailPrivateLinkForm').trigger('submit');
+				dialog.$el.find('#emailButton').trigger('click');
 
 				expect(sendEmailPrivateLinkStub.callCount).toEqual(1);
 				expect(dialog.$el.find('.emailPrivateLinkForm .emailField').val()).toEqual('Sending ...');