Fix warnings

Author: greglittlefield-wf

example/test/get_dom_node_test.dart

@@ -40,11 +40,11 @@ class _SimpleComponent extends react.Component2 {
   var refToElement;
 
   @override
-  componentWillUnmount() => print("unmount");
+  componentWillUnmount() => print('unmount');
 
   @override
   componentDidMount() {
-    print("mount");
+    print('mount');
     customAssert('ref to span return span ', refToSpan.text == 'Test');
     // ignore: deprecated_member_use_from_same_package
     customAssert('findDOMNode works on this', react_dom.findDOMNode(this) != null);

example/test/unmount_test.dart

@@ -8,7 +8,7 @@ var SimpleComponent = react.registerComponent2(() => _SimpleComponent());
 
 class _SimpleComponent extends react.Component2 {
   @override
-  componentDidMount() => print("mount");
+  componentDidMount() => print('mount');
 
   @override
   componentWillUnmount() => print('unmount');

lib/react_dom.dart

@@ -5,8 +5,6 @@
 library react_dom;
 
 // ignore: deprecated_member_use_from_same_package
-import 'dart:html';
-
 import 'package:react/react.dart' show Component;
 import 'package:react/react_client/react_interop.dart' show ReactDom;
 import 'package:react/src/react_client/create_root.dart' show ReactRoot, createRoot;

lib/react_test_utils.dart

@@ -37,7 +37,7 @@ import 'package:react/src/react_test_utils/internal_test_utils.dart' as itu;
 /// * For DOM components, this with return the String corresponding to its tagName ('div', 'a', etc.).
 /// * For custom composite components React.createClass()-based components, this will return the [ReactClass].
 @Deprecated('Use the react_testing_library package instead.')
-final getComponentTypeV2 = itu.getComponentTypeV2;
+const getComponentTypeV2 = itu.getComponentTypeV2;
 
 @Deprecated('Use the react_testing_library package instead.')
 typedef ComponentTestFunction = bool Function(dynamic /* [1] */ component);
@@ -155,17 +155,17 @@ external dynamic /* [1] */ _findRenderedComponentWithType(/* [1] */ tree, dynami
 /// Returns true if element is a composite component.
 /// (created with React.createClass()).
 @Deprecated('Use the react_testing_library package instead.')
-final isCompositeComponent = itu.isCompositeComponent;
+const isCompositeComponent = itu.isCompositeComponent;
 
 /// Returns `true` if instance is a custom composite component created using `React.createClass()`
 /// that is of the [ReactComponentFactoryProxy.type] of the provided [componentFactory].
 @Deprecated('Use the react_testing_library package instead.')
-final isCompositeComponentWithTypeV2 = itu.isCompositeComponentWithTypeV2;
+const isCompositeComponentWithTypeV2 = itu.isCompositeComponentWithTypeV2;
 
 /// Returns true if instance is a DOM component (such as a <div> or <span>).
 @JS('React.addons.TestUtils.isDOMComponent')
 @Deprecated('Use the react_testing_library package instead.')
-final isDOMComponent = itu.isDOMComponent;
+const isDOMComponent = itu.isDOMComponent;
 
 /// Returns true if [object] is a valid React component.
 @JS('React.addons.TestUtils.isElement')
@@ -175,7 +175,7 @@ external bool isElement(dynamic object);
 /// Returns `true` if [element] is a [ReactElement]
 /// that is of the [ReactComponentFactoryProxy.type] of the provided [componentFactory].
 @Deprecated('Use the react_testing_library package instead.')
-final isElementOfTypeV2 = itu.isElementOfTypeV2;
+const isElementOfTypeV2 = itu.isElementOfTypeV2;
 
 @JS('React.addons.TestUtils.scryRenderedComponentsWithType')
 external List<dynamic> /* [1] */ _scryRenderedComponentsWithType(/* [1] */ tree, dynamic type);

lib/src/react_client/private_utils.dart

@@ -58,10 +58,9 @@ void validateJsApi() {
     createReactDartComponentClass(null, null, null);
     createReactDartComponentClass2(null, null, null);
     _isJsApiValid = true;
-  } on NoSuchMethodError catch (e) {
+  } on NoSuchMethodError catch (_) {
     throw Exception('react.js and react_dom.js must be loaded.');
   } catch (_) {
-    rethrow;
     throw Exception('Loaded react.js must include react-dart JS interop helpers.');
   }
 }