Add tests

Author: Yui T

src/compiler/emitter.ts

@@ -3889,7 +3889,7 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
                         // We create a synthetic copy of the identifier in order to avoid the rewriting that might
                         // otherwise occur when the identifier is emitted.
                         index = <Identifier | LiteralExpression>createSynthesizedNode(propName.kind);
-                        (<Identifier | LiteralExpression>index).text = (<Identifier | LiteralExpression>propName).text;
+                        (<Identifier | LiteralExpression>index).text = unescapeIdentifier((<Identifier | LiteralExpression>propName).text);
                     }
 
                     return !nameIsComputed && index.kind === SyntaxKind.Identifier

src/compiler/utilities.ts

@@ -238,11 +238,10 @@ namespace ts {
             return identifier.charCodeAt(0) === CharacterCodes._ && identifier.charCodeAt(1) === CharacterCodes._ ? true : false;
         }
     }
-    
+
     // Add an extra underscore to identifiers that start with two underscores to avoid issues with magic names like '__proto__'
-    // TODO(yuisu): comment
     export function escapeIdentifier(identifier: string): string {
-        return prefixWithUnderscoreUnderscore(identifier)? "_" + identifier : identifier;
+        return prefixWithUnderscoreUnderscore(identifier) ? "_" + identifier : identifier;
     }
 
     // Remove extra underscore from escaped identifier