Gracefully handle accessor declarations in ambient classes.

src/compiler/checker.ts

@@ -4948,7 +4948,7 @@ module ts {
             }
 
             checkSourceElement(node.body);
-            if (node.type) {
+            if (node.type && !isAccessor(node.kind)) {
                 checkIfNonVoidFunctionHasReturnExpressionsOrSingleThrowStatment(node, getTypeFromTypeNode(node.type));
             }
 

src/compiler/parser.ts

@@ -2902,7 +2902,16 @@ module ts {
             node.typeParameters = sig.typeParameters;
             node.parameters = sig.parameters;
             node.type = sig.type;
-            node.body = parseBody(/* ignoreMissingOpenBrace */ false);
+
+            // A common error is to try to declare an accessor in an ambient class.
+            if (inAmbientContext && canParseSemicolon()) {
+                parseSemicolon();
+                node.body = createMissingNode();
+            }
+            else {
+                node.body = parseBody(/* ignoreMissingOpenBrace */ false);
+            }
+
             return finishNode(node);
         }