WebKit, llvm, are pretty important in that they altered the fundamental of present day by being so openly used. It's apples ehm to oranges at that level, but what has Google contributes of the likes?
Easy. Android (Open Source, while the source is not always released right after a new version is out), running on most Smartphones over the world. Pretty big contribution I'd say, especially in a world turning Mobile-First. Chromium. Go. I'd say their contributions are far from negligible.
They might have contributed the most over time, but we probably don't disagree who was more important to the whole WebKit party getting going.
The KHTML developers?
Android, Chromium, V8, Go, Dart, Guava, Guice, GWT, Angular, Polymer, Blink, WebM, and probably hundreds of libraries.
Android sadly is not OSS, just like OSX isn't, even though it's obviously based on it. Chromium was V8 and WebKit, and so depended on WebKit. The rest are obviously not fundamental pieces of technology.
How are those other open source projects not "fundamental"?
Android sadly is not OSS
"Android" can have conflicting definitions, but AOSP is certainly OSS.
Apple did the absolute minimum with WebKit source (occasional tarball dumps) until a KHTML developer's rant shamed them into being a bit better. LLVM has become a valuable project but I think mostly by luck; Apple contributed some funding to it because they didn't want to make the patent promises they would need to to distribute GCC. Neither of these is a new project that was developed by Apple and then released, in contrast to mda's list.