[3P] Add touch support

[aee-google]

Bug: 447659892

[github-actions]

🤖 Gemini Suggested Commit Message

---

starboard: Add support for touch input

Integrate Starboard touch input events into Cobalt's UI event
pipeline. This change maps kSbInputEventTypePress,
kSbInputEventTypeUnpress, and kSbInputEventTypeMove to the
corresponding ui::TouchEvent types, enabling applications to
respond to touch screen and touch pad interactions.

Bug: 447659892

---

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[gemini-code-assist]

Code Review

This pull request adds support for touch events by creating ui::TouchEvent from Starboard input events. The implementation has a few issues. There's a critical bug in a debug build that can cause a crash due to incorrect ordering of null checks and DCHECKs. Another critical issue is a potential use of an uninitialized variable in release builds if an unknown event type is received. I've also pointed out some areas for improvement, such as removing redundant logging and replacing a magic number with a named constant for better readability. Please address the critical issues and consider the other suggestions.

[andrewsavage1]

In general we're replacing DCHECKs with CHECKs (see b/435425692), should we do the same here?

[aee-google]

🤷

[andrewsavage1]

Wdyt about making this a CHECK for now instead? We can always change back if it seems like it causes crashes we could avoid otherwise (cc @jellefoks who I think wrote this code originally)