Stream JSON output (--json)

This fixes webpack#4629

JSON.stringify can fail with `RangeError: Invalid string length`
when it runs out of memory. See nodejs/node-v0.x-archivei#14170.
With this fix, I was able to write out the profile JSON without
errors.

bin/webpack.js

@@ -334,7 +334,10 @@ function processOptions(options) {
 			process.exit(1); // eslint-disable-line
 		}
 		if(outputOptions.json) {
-			process.stdout.write(JSON.stringify(stats.toJson(outputOptions), null, 2) + "\n");
+			var stringify = require('JSONStream').stringify('', '', '');
+			stringify.pipe(process.stdout);
+			stringify.write(stats.toJson(outputOptions));
+			stringify.end();
 		} else if(stats.hash !== lastHash) {
 			lastHash = stats.hash;
 			process.stdout.write(stats.toString(outputOptions) + "\n");

package.json

@@ -4,6 +4,7 @@
   "author": "Tobias Koppers @sokra",
   "description": "Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.",
   "dependencies": {
+    "JSONStream": "^1.3.1",
     "acorn": "^5.0.0",
     "acorn-dynamic-import": "^2.0.0",
     "ajv": "^4.7.0",