Crash report: `ReferenceError: Can't find variable: ResizeObserver`

URL

https://app.uniswap.org/#/swap?chain=mainnet

swap state

{
  "INPUT": {
    "currencyId": "ETH"
  },
  "independentField": "INPUT",
  "recipient": null,
  "typedValue": "5",
  "OUTPUT": {
    "currencyId": "0x111111111117dC0aa78b770fA6A738034120C302"
  }
}

Error

ReferenceError: Can't find variable: ResizeObserver

Stacktrace

https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:1948097
https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:1947819
https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:1947932
Uu@https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:2138025
Uu@[native code]
unstable_runWithPriority@https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:2157236
Du@https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:2134645
wu@https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:2130731
wu@[native code]
https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:2079999
unstable_runWithPriority@https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:2157236
Xf@https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:2079945
Yf@https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:2079880
bu@https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:2127883
Ca@https://app.uniswap.org/static/js/3.41f60794.chunk.js:2:2099533
Ca@[native code]
https://app.uniswap.org/static/js/main.2f16c543.chunk.js:1:34964

Device data

{
  "ua": "Mozilla/5.0 (iPhone; CPU iPhone OS 12_5 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) CriOS/92.0.4515.90 Mobile/15E148 Safari/604.1",
  "browser": {
    "name": "Chrome",
    "version": "92.0.4515.90",
    "major": "92"
  },
  "engine": {
    "name": "WebKit",
    "version": "605.1.15"
  },
  "os": {
    "name": "iOS",
    "version": "12.5"
  },
  "device": {
    "vendor": "Apple",
    "model": "iPhone",
    "type": "mobile"
  },
  "cpu": {}
}

No source file or test is named; begin by reproducing the swap page crash on iOS 12.5 with the reported device and tracing the deployed stack's ResizeObserver reference back to the source. Done means the swap page loads without this ReferenceError on that environment, with a regression check added if the project has an applicable test location.