[libdylink.js] Avoid string key for private field. NFC (#24915)

Author: sbc100

src/lib/libdylink.js

@@ -14,18 +14,18 @@ var LibraryDylink = {
 #if FILESYSTEM
   $registerWasmPlugin__deps: ['$preloadPlugins'],
   $registerWasmPlugin: () => {
-    // Use string keys here to avoid minification since the plugin consumer
-    // also uses string keys.
+    // Use string keys here for public methods to avoid minification since the
+    // plugin consumer also uses string keys.
     var wasmPlugin = {
-      'promiseChainEnd': Promise.resolve(),
+      promiseChainEnd: Promise.resolve(),
       'canHandle': (name) => {
         return !Module['noWasmDecoding'] && name.endsWith('.so')
       },
       'handle': (byteArray, name, onload, onerror) => {
         // loadWebAssemblyModule can not load modules out-of-order, so rather
         // than just running the promises in parallel, this makes a chain of
         // promises to run in series.
-        wasmPlugin['promiseChainEnd'] = wasmPlugin['promiseChainEnd'].then(
+        wasmPlugin.promiseChainEnd = wasmPlugin.promiseChainEnd.then(
           () => loadWebAssemblyModule(byteArray, {loadAsync: true, nodelete: true}, name, {})).then(
             (exports) => {
 #if DYLINK_DEBUG

test/code_size/test_codesize_hello_dylink.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 27021,
-  "a.out.js.gz": 11470,
+  "a.out.js": 26982,
+  "a.out.js.gz": 11461,
   "a.out.nodebug.wasm": 18561,
   "a.out.nodebug.wasm.gz": 9167,
-  "total": 45582,
-  "total_gz": 20637,
+  "total": 45543,
+  "total_gz": 20628,
   "sent": [
     "__heap_base",
     "__indirect_function_table",

test/code_size/test_codesize_hello_dylink_all.json

@@ -1,7 +1,7 @@
 {
-  "a.out.js": 246838,
+  "a.out.js": 246799,
   "a.out.nodebug.wasm": 597826,
-  "total": 844664,
+  "total": 844625,
   "sent": [
     "IMG_Init",
     "IMG_Load",