16849 Avoid using Dart_New for semantics (cla: yes, waiting for tree to go green)

16850 shake out Paint.toString (cla: yes, perf: app size, severe: performance)

16851 Roll src/third_party/dart c790e0c4017d..dda5bcee00d3 (5 commits) (cla: yes, waiting for tree to go green)

16852 Roll src/third_party/skia 0a3900fb33dc..bde9fcce155f (1 commits) (cla: yes, waiting for tree to go green)

16853 Roll src/third_party/skia bde9fcce155f..55f681faf391 (2 commits) (cla: yes, waiting for tree to go green)