Implement try/catch in the JS backend.

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library code_generator;
 
 import 'glue.dart';
 
 import '../../tree_ir/tree_ir_nodes.dart' as tree_ir;
 import '../../js/js.dart' as js;
@@ skipping 407 matching lines @@
   @override
   void visitExpressionStatement(tree_ir.ExpressionStatement node) {
     accumulator.add(new js.ExpressionStatement(
         visitExpression(node.expression)));
     visitStatement(node.next);
   }
 
   @override
   void visitIf(tree_ir.If node) {
     accumulator.add(new js.If(visitExpression(node.condition),
-                              buildBody(node.thenStatement),
-                              buildBody(node.elseStatement)));
+                              buildBodyStatement(node.thenStatement),
+                              buildBodyStatement(node.elseStatement)));
   }
 
   @override
   void visitLabeledStatement(tree_ir.LabeledStatement node) {
-    accumulator.add(buildLabeled(() => buildBody(node.body),
+    accumulator.add(buildLabeled(() => buildBodyStatement(node.body),
                                  node.label,
                                  node.next));
     visitStatement(node.next);
   }
 
   js.Statement buildLabeled(js.Statement buildBody(),
                 tree_ir.Label label,
                 tree_ir.Statement fallthroughStatement) {
     tree_ir.Statement savedFallthrough = fallthrough;
     fallthrough = fallthroughStatement;
@@ skipping 24 matching lines @@
     if (accumulator.length == 0) {
       return new js.EmptyStatement();
     }
     if (accumulator.length == 1) {
       return accumulator.single;
     }
     return new js.Block(accumulator);
   }
 
   /// Builds a nested statement.
-  js.Statement buildBody(tree_ir.Statement statement) {
+  js.Statement buildBodyStatement(tree_ir.Statement statement) {
     List<js.Statement> savedAccumulator = accumulator;
-    accumulator = new List<js.Statement>();
+    accumulator = <js.Statement>[];
     visitStatement(statement);
     js.Statement result = _bodyAsStatement();
     accumulator = savedAccumulator;
     return result;
   }
 
+  js.Block buildBodyBlock(tree_ir.Statement statement) {
+    List<js.Statement> savedAccumulator = accumulator;
+    accumulator = <js.Statement>[];
+    visitStatement(statement);
+    js.Statement result = new js.Block(accumulator);
+    accumulator = savedAccumulator;
+    return result;
+  }
+
   js.Statement buildWhile(js.Expression condition,
                           tree_ir.Statement body,
                           tree_ir.Label label,
                           tree_ir.Statement fallthroughStatement) {
-    return buildLabeled(() => new js.While(condition, buildBody(body)),
+    return buildLabeled(() => new js.While(condition, buildBodyStatement(body)),
                         label,
                         fallthroughStatement);
   }
 
   @override
   void visitWhileCondition(tree_ir.WhileCondition node) {
     accumulator.add(
         buildWhile(visitExpression(node.condition),
                    node.body,
                    node.label,
                    node));
     visitStatement(node.next);
   }
 
   @override
   void visitWhileTrue(tree_ir.WhileTrue node) {
     accumulator.add(
         buildWhile(new js.LiteralBool(true), node.body, node.label, node));
   }
 
   @override
   void visitReturn(tree_ir.Return node) {
     accumulator.add(new js.Return(visitExpression(node.value)));
   }
 
   @override
   void visitTry(tree_ir.Try node) {
-    // TODO(kmillikin): implement TryStatement.
-    return giveup(node);
+    js.Block tryBlock = buildBodyBlock(node.tryBody);
+    tree_ir.Variable exceptionVariable = node.catchParameters.first;
+    js.VariableDeclaration exceptionParameter =
+        new js.VariableDeclaration(getVariableName(exceptionVariable));
+    js.Block catchBlock = buildBodyBlock(node.catchBody);
+    js.Catch catchPart = new js.Catch(exceptionParameter, catchBlock);
+    accumulator.add(new js.Try(tryBlock, catchPart, null));
   }
 
   @override
   js.Expression visitCreateBox(tree_ir.CreateBox node) {
     return new js.ObjectInitializer([]);
   }
 
   @override
   js.Expression visitCreateInstance(tree_ir.CreateInstance node) {
     ClassElement cls = node.classElement;
@@ skipping 94 matching lines @@
 
   @override
   visitVariableDeclaration(tree_ir.VariableDeclaration node) {
     return errorUnsupportedNode(node);
   }
 
   errorUnsupportedNode(tree_ir.DartSpecificNode node) {
     throw "Unsupported node in JS backend: $node";
   }
 }