Fixes issues with uglify.js usage

Summary: Adds flow type defs for uglify, and fixes the two issues found

Reviewed By: jeanlauliac

Differential Revision: D5029190

fbshipit-source-id: eb5947b051844938da241e002b727edc1384e3a6

packager/src/ModuleGraph/types.flow.js

@@ -110,7 +110,7 @@ export type TransformResult = {|
   code: string,
   dependencies: Array<string>,
   dependencyMapName?: string,
-  map: ?Object,
+  map: ?MappingsMap,
 |};
 
 export type TransformResults = {[string]: TransformResult};

packager/src/ModuleGraph/worker/optimize-module.js

@@ -19,6 +19,7 @@ const minify = require('../../JSTransformer/worker/minify');
 const sourceMap = require('source-map');
 
 import type {TransformedSourceFile, TransformResult} from '../types.flow';
+import type {MappingsMap, SourceMap} from '../../lib/SourceMap';
 
 export type OptimizationOptions = {|
   dev: boolean,
@@ -71,7 +72,7 @@ function optimize(transformed, file, originalCode, options): TransformResult {
     gen.code,
     inputMap && mergeSourceMaps(file, inputMap, gen.map),
   );
-  return {code: min.code, map: inputMap && min.map, dependencies};
+  return {code: min.code, map: min.map, dependencies};
 }
 
 function optimizeCode(code, map, filename, inliningOptions) {
@@ -86,7 +87,11 @@ function optimizeCode(code, map, filename, inliningOptions) {
   });
 }
 
-function mergeSourceMaps(file, originalMap, secondMap) {
+function mergeSourceMaps(
+  file: string,
+  originalMap: SourceMap,
+  secondMap: SourceMap,
+): MappingsMap {
   const merged = new sourceMap.SourceMapGenerator();
   const inputMap = new sourceMap.SourceMapConsumer(originalMap);
   new sourceMap.SourceMapConsumer(secondMap)