[dart2js] Reduce size of Dart2JS deferred loading event logs.

- Only include the script tag src if it differs from the previous log entry.
- Use single letters for each event field's key.
- Fix some typos.
- Remove 'uri' from download event as it can be inferred from script tag src and part file name.

Change-Id: Ib7916ea5e92720a10c7e1e1cab2e535fae2bbf49
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/311180
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Commit-Queue: Nate Biggs <natebiggs@google.com>

pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart

@@ -381,7 +381,7 @@ class ModelEmitter {
       {js.Expression? code}) {
     return js.js.statement(
         '((s,d,e) => {s[d] = s[d] || {}; s[d][e] = s[d][e] || [];'
-        's[d][e].push({part:#part,event:"beginLoadPart"});})'
+        's[d][e].push({p:#part,e:"beginPart"});})'
         '(self,#deferredInitializers, #eventLog)',
         {
           'deferredInitializers': js.string(deferredInitializersGlobal),
@@ -605,7 +605,7 @@ var ${startupMetricsGlobal} =
     // Now we copy the deferredInitializer.current into its correct hash.
     final epilogue = js.js.statement(
         '((d,h)=>{d[h]=d.current; '
-        'd.#eventLog.push({hash:h,event:"endPartLoad",part:#part})})'
+        'd.#eventLog.push({p:#part,e:"endPart",h:h})})'
         '(#deferredInitializers,#hash)',
         {
           'deferredInitializers': deferredInitializersGlobal,

pkg/compiler/test/dump_info/data/deferred/main.dart

@@ -104,7 +104,7 @@
   "id": "outputUnit/1",
   "kind": "outputUnit",
   "name": "1",
-  "size": 1255,
+  "size": 1230,
   "filename": "out_1.part.js",
   "imports": [
     "lib"

pkg/compiler/test/dump_info/data/deferred_future/main.dart

@@ -110,7 +110,7 @@
   "id": "outputUnit/1",
   "kind": "outputUnit",
   "name": "1",
-  "size": 977,
+  "size": 952,
   "filename": "out_1.part.js",
   "imports": [
     "lib1"

sdk/lib/_internal/js_runtime/lib/js_helper.dart

@@ -2794,14 +2794,13 @@ DeferredLoadCallback? deferredLoadHook;
 void _addEvent(
     {required String part,
     required String event,
-    String? hash,
-    String? uri,
-    String? context}) {
+    String? loadId,
+    String? hash}) {
   var initializationEventLog = JS_EMBEDDED_GLOBAL('', INITIALIZATION_EVENT_LOG);
-  var dataObj = JS('=Object', '{part: #, event: #}', part, event);
-  if (hash != null) JS('', '#.hash = #', dataObj, hash);
-  if (uri != null) JS('', '#.uri = #', dataObj, uri);
-  if (context != null) JS('', '#.context = #', dataObj, context);
+  var dataObj = JS('=Object', '{p: #, e: #}', part, event);
+  if (hash != null) JS('', '#.h = #', dataObj, hash);
+  if (loadId != null) JS('', '#.l = #', dataObj, loadId);
+  JS('', '#.s = #', dataObj, thisScript);
   JS('', '#.push(#)', initializationEventLog, dataObj);
 }
 
@@ -2811,16 +2810,17 @@ void _addEvent(
 /// truncated, the newest events are retained.
 String _getEventLog() {
   var initializationEventLog = JS_EMBEDDED_GLOBAL('', INITIALIZATION_EVENT_LOG);
-  final log = JS(
-      'String',
-      'Array.from(#)'
-          '.map(((s) => '
-          '(e, i) => { e.index = i; e.s = s; return e; })(#))'
-          '.reverse()'
-          '.map((e) => JSON.stringify(e)).join("\\n")',
-      initializationEventLog,
-      thisScript);
-  return log;
+  final o = JS('', 'Array.from(#).reverse()', initializationEventLog);
+  JS(
+      '',
+      '#.reduce((p, e, i, a) => {e.i = a.length - i; '
+          'if (p == null) return e.s; '
+          'if (e.s == null) return p; '
+          'if (e.s === p) { delete e.s; return p; }'
+          'return e.s;}'
+          ', null)',
+      o);
+  return JS('String', '#.map((e) => JSON.stringify(e)).join("\\n")', o);
 }
 
 /// Loads a deferred library. The compiler generates a call to this method to
@@ -2877,16 +2877,17 @@ Future<Null> loadDeferredLibrary(String loadId, int priority) {
       var uri = uris[i];
       var hash = hashes[i];
       if (JS('bool', '#(#)', isHunkInitialized, hash)) {
-        _addEvent(part: uri, hash: hash, event: 'alreadyInitialized');
+        _addEvent(
+            part: uri, hash: hash, event: 'alreadyInitialized', loadId: loadId);
         continue;
       }
       // On strange scenarios, e.g. if js encounters parse errors, we might get
       // an "success" callback on the script load but the hunk will be null.
       if (JS('bool', '#(#)', isHunkLoaded, hash)) {
-        _addEvent(part: uri, hash: hash, event: 'initilize');
+        _addEvent(part: uri, hash: hash, event: 'initialize', loadId: loadId);
         JS('void', '#(#)', initializer, hash);
       } else {
-        _addEvent(part: uri, hash: hash, event: 'missing');
+        _addEvent(part: uri, hash: hash, event: 'missing', loadId: loadId);
 
         throw new DeferredLoadException("Loading ${uris[i]} failed: "
             "the code with hash '${hash}' was not loaded.\n"
@@ -3060,9 +3061,9 @@ Future<Null> _loadHunk(String hunkName, String loadId, int priority) {
   var initializationEventLog = JS_EMBEDDED_GLOBAL('', INITIALIZATION_EVENT_LOG);
 
   var future = _loadingLibraries[hunkName];
-  _addEvent(part: hunkName, event: 'startLoad');
+  _addEvent(part: hunkName, event: 'startLoad', loadId: loadId);
   if (future != null) {
-    _addEvent(part: hunkName, event: 'reuse');
+    _addEvent(part: hunkName, event: 'reuse', loadId: loadId);
     return future.then((Null _) => null);
   }
 
@@ -3072,22 +3073,23 @@ Future<Null> _loadHunk(String hunkName, String loadId, int priority) {
   // sanitized URL.
   String uriAsString = JS('', '#.toString()', trustedScriptUri);
 
-  _addEvent(part: hunkName, uri: uriAsString, event: 'download');
+  _addEvent(part: hunkName, event: 'download', loadId: loadId);
 
   var deferredLibraryLoader = JS('', 'self.dartDeferredLibraryLoader');
   Completer<Null> completer = Completer();
 
   void success() {
-    _addEvent(part: hunkName, event: 'downloadSuccess');
+    _addEvent(part: hunkName, event: 'downloadSuccess', loadId: loadId);
     completer.complete(null);
   }
 
   void failure(error, String context, StackTrace? stackTrace) {
-    _addEvent(part: hunkName, context: context, event: 'downloadFailure');
+    _addEvent(part: hunkName, event: 'downloadFailure', loadId: loadId);
     _loadingLibraries[hunkName] = null;
     stackTrace ??= StackTrace.current;
     completer.completeError(
         DeferredLoadException('Loading $uriAsString failed: $error\n'
+            'Context: $context\n'
             'event log:\n${_getEventLog()}\n'),
         stackTrace);
   }