[RPP] Fix source maps not being loaded in enhanced traces

http://crrev.com/c/6955443 refactored EnhancedTracesParser to use a
TraceObject, but there was a subtle bug that caused TraceObject to never
have any metadata (which is where the source maps live).

Bug: 427455148
Change-Id: I417b567ca034c1a223eb53cdd5a08467f4d7b8ca
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/7028254
Commit-Queue: Connor Clark <cjamcl@chromium.org>
Auto-Submit: Connor Clark <cjamcl@chromium.org>
Reviewed-by: Paul Irish <paulirish@chromium.org>

Author: Connor Clark

front_end/core/sdk/RehydratingConnection.snapshot.txt

@@ -420,7 +420,7 @@ Content:
     "url": "https://www.paulirish.com/javascripts/firebase-performance-standalone.js",
     "hasSourceURL": false,
     "sourceURL": "",
-    "sourceMapURL": "firebase-performance-standalone.js.map",
+    "sourceMapURL": "data:application/json;charset=utf-8,%7B%22version%22%3A3%2C%22file%22%3A%22firebase-performance-standalone.js%22%2C%22sources%22%3A%5B%22..%2F..%2Fnode_modules%2Ftslib%2Ftslib.es6.js%22%2C%22..%2Futil…",
     "pid": 97964,
     "sourceText": "!function(e,t){\"obje…",
     "length": 48248,

front_end/core/sdk/RehydratingConnection.test.ts

@@ -282,6 +282,9 @@ describeWithEnvironment('RehydratingConnection emittance', () => {
       if (typeof m === 'object' && m.params?.sourceText) {
         m.params.sourceText = m.params.sourceText.slice(0, 20) + '…';
       }
+      if (typeof m === 'object' && m.params?.sourceMapURL && m.params.sourceMapURL.length > 200) {
+        m.params.sourceMapURL = m.params.sourceMapURL.slice(0, 200) + '…';
+      }
       // @ts-expect-error
       if (typeof m === 'object' && m.result?.scriptSource) {
         // @ts-expect-error

front_end/core/sdk/TraceObject.ts

@@ -14,13 +14,14 @@ import type {SourceMapV3} from './SourceMap.js';
 export class TraceObject {
   readonly traceEvents: Protocol.Tracing.DataCollectedEvent['value'];
   readonly metadata: {sourceMaps?: Array<{sourceMapUrl: string, sourceMap: SourceMapV3, url: string}>};
-  constructor(payload: Protocol.Tracing.DataCollectedEvent['value']|TraceObject, meta: Object = {}) {
-    // Handle the typical traceEvent array juggling here.
-    const events = Array.isArray(payload) ? payload : payload.traceEvents;
-    const metadata = meta ?? (!Array.isArray(payload) && payload.metadata) ?? {};
-
-    this.traceEvents = events;
-    this.metadata = metadata;
+  constructor(payload: Protocol.Tracing.DataCollectedEvent['value']|TraceObject, meta?: Object) {
+    if (Array.isArray(payload)) {
+      this.traceEvents = payload;
+      this.metadata = meta ?? {};
+    } else {
+      this.traceEvents = payload.traceEvents;
+      this.metadata = payload.metadata;
+    }
   }
 }