17634 Always build GTK shell (cla: yes, waiting for tree to go green)

17635 reduce web shard count from 8 to 4 (cla: yes)

17638 Roll src/third_party/skia f7255d72f8da..96bfeff55c58 (4 commits) (cla: yes, waiting for tree to go green)

17639 Roll src/third_party/skia 96bfeff55c58..801ba0d6064f (8 commits) (cla: yes, waiting for tree to go green)

17640 Roll fuchsia/sdk/core/linux-amd64 from VzWN4… to LnaL2… (cla: yes)

17643 Implement Hashcode for TextEditingValue in InputConnectionAdaptor (cla: yes, waiting for tree to go green)