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

URL

https://app.uniswap.org/#/swap?use=V2&chain=mainnet

swap state

{
  "INPUT": {
    "currencyId": "ETH"
  },
  "independentField": "INPUT",
  "recipient": null,
  "OUTPUT": {
    "currencyId": "0x08AD83D779BDf2BBE1ad9cc0f78aa0D24AB97802"
  },
  "typedValue": "1"
}

Error

ReferenceError: Can't find variable: ResizeObserver

Stacktrace

https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2704029
https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2703665
https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2703388
rs@https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2878955
Su@https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2899168
su@https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2891425
su@[native code]
qf@https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2832151
https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2897964
_u@https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2897967
fu@https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2890427
fu@[native code]
S@https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2916279
M@https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2916813
https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2920247
c@https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2920361
n@https://app.uniswap.org/static/js/2.c33fc571.chunk.js:2:2919307

Device data

{
  "ua": "Mozilla/5.0 (iPhone; CPU iPhone OS 12_5_5 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/12.1.2 Mobile/15E148 Safari/604.1",
  "browser": {
    "name": "Mobile Safari",
    "version": "12.1.2",
    "major": "12"
  },
  "engine": {
    "name": "WebKit",
    "version": "605.1.15"
  },
  "os": {
    "name": "iOS",
    "version": "12.5.5"
  },
  "device": {
    "vendor": "Apple",
    "model": "iPhone",
    "type": "mobile"
  },
  "cpu": {}
}

Start by reproducing the crash at the reported app.uniswap.org swap URL using Mobile Safari on iOS 12.5.5, then trace the ResizeObserver reference from static/js/2.c33fc571.chunk.js:2 back to its source. Done means the swap page loads without this ReferenceError on the reported browser and the affected behavior is covered by a regression check.