This won't happen. The platform default is one of the most decisive factor for the market share and Apple has a full control here. Unless they do a critical mistake at IE6 level, Chrome won't likely have above 10% iOS market share.
That statement is much, much less true than it once was -- some quick searching puts Chrome at about 66% of desktop market share (despite neither of the two dominant desktop OSes shipping Chrome as a default), and the two default options (Chromium-based Edge and Safari) combining for about 25% of desktop market share.
Apple did learn from this mistake and kept a minimal level of investment as well as prohibited competition via full control of App Store, which effectively forced most websites to support WebKit. Even though they did not invest that much on Safari over a similar length of period through these ways and still maintains the lead on MacOS. Which in fact proves my point.