This is more or less my memory of the fork. Google were a major contributor, wanted to make some different decisions in various places to Apple and spent lots o

This is more or less my memory of the fork. Google were a major contributor, wanted to make some different decisions in various places to Apple and spent lots of time trying to make Apple happy, and concluded the quickest way to make progress was to fork and not have to convince other contributors (even with the resultant loss of contributions from others). Opera is indeed built on the Chromium content API (v. the Chromium Embedded Framework, which provides a stable API but was less power), and that was a design choice made prior to the Blink fork and hence why Opera followed Google to Blink.