Google Docs. There was nothing else like this when Google launched it. (Or at least that most people were aware of.)
Google Docs originated from two separate products that Google bought: Writely and XL2Web...
Google Maps. When Google launched Google Maps where you could click and drag in the map, it was revolutionary. MapQuest and everything else just uses static images. Then they added Streetview. Now it's the clear leader in maps.
Google Maps was designed and sold to Google by 2 Danish brothers at a Sydney-based company called "Where 2 Technologies" Google then bought and added bits of Keyhole (geospatial data and sat imagery company), which is where the click-and-drag came from. Then they bought a company called ZipDash to provide the traffic analysis...
Android. Yes, they bought this one, but without Google's commitment, it wouldn't be anything close to where it is today.
Like you said: they bought this one too
Chromebooks. Google owns the low-end laptop ecosystem.
No, they don't. They own the OS for the low-end netbook ecosystem (since they're so low-end you can't call it a laptop). They don't make or design the hardware (except for a few "Pixel" books that went nowhere), and the only place this ecosystem seems to matter is the education ecosystem...
Chrome Browser. Google is clearly dominant in the browser market.
True enough for now. Worth noting: it built with free software components from Apple WebKit and Mozilla Firefox...
GMail. They took the idea of Hotmail, but did it better.
All they really did was write a web page that didn't have to reload the entire page and add a search bar. But I'm beginning to see a pattern of "they took the idea of...."
YouTube. Yes, this was an acquisition where Google Video was failing, but they've done quite well with it.
So they failed to do it, and bought someone else who succeeded. Seems to fit the pattern...
Why do so many thing on your list of Google "successes" start with buying the people who actually innovated it?