Change kMaxFramebufferObservation to 4K. (#2350)
Change kMaxFramebufferObservation to 4K. (#2350)

Framebuffer observation should support at least 1080p.
Validate framebuffer against a downscaled version is sub-optimal, and most desktop app runs at 720p/1080p.
google/agi,pmuetschard/gapid,Qining/gapid,Qining/gapid,Qining/gapid,pmuetschard/gapid,google/gapid,google/agi,google/gapid,google/gapid,google/gapid,Qining/gapid,pmuetschard/gapid,google/gapid,google/agi,google/gapid,Qining/gapid,Qining/gapid,Qining/gapid,google/gapid,pmuetschard/gapid,Qining/gapid,google/agi,pmuetschard/gapid,google/agi,pmuetschard/gapid,pmuetschard/gapid,google/agi,google/agi,google/gapid,google/agi,pmuetschard/gapid