The hint comes from Google's Android P Beta 2. XDA Developers spent some time digging through the Google code and found evidence that Google may be adding support for a new wireless charging dock. The code uses references like "com.google" instead of "com.android" when describing the wireless charger, which could mean that it's made specifically for Google products or is Google branded.
Earlier Pixel 3 leaks claim that the phone may come with a glass back, which could point to wireless charging. For a variety of reasons, phone manufacturers generally don't offer wireless charging in phones with metal bodies, and glass is a good casing alternative to metal. (But not every glass-backed phone comes with wireless charging though).
Years ago, Google phones (like the Google Nexus 6 and Google Nexus 5) had wireless charging, but the feature was absent in Google's 2015 phones (the Nexus 5X and Nexus 6P) and hasn't come back since. But Google may bring it back to compete with the iPhone 8 and iPhone X, which finally added wireless charging to Apple's phones in 2017.
XDA Developers also reports that the Pixel 3 could have squeezable sides. This feature appeared on the Google Pixel 2 as a quick way to launch the Google Assistant. Squeezable sides also appeared on the HTC U11, but you could customize which app was launched when squeezed. Since HTC's engineers also work on Google's Pixel phones, perhaps the feature will get some added functions if it comes to the Pixel 3.
Google didn't immediately respond to a request for comment.