* Add framework-side support for system text scale factor.
* Rolling engine to e3404b81a53ba3180c7623a6f2190ebb28518f30
Additional changes rolled in with engine change:
libtxt: implementation of GetRectsForRange that processes a line at a time - e3404b8
Provide an entropy source to the Dart engine (#4161) - e1aa867
libtxt: search for fallback fonts that can match emoji and CJK characters - 8061df1
Roll skia to e4679fa06a. (#4157) - 267e7a8
Update buildroot to 53fea9aebb (#4160) - 02ea7ae
Revert engine Dart roll. (#4158) - 14aab33
Add support for system text scale factor. (#4124) - b2a7f4b
Include _http into sky_engine libraries for analyzer (#4154) - b930f10
libtxt: Remove postprocess_line and improve tracking of X offsets - 86f95f0
libtxt: remove redundant line_widths (#4152) - 14bf515
Roll dart to ade37f931e90b0fdb8fe16d6bf6f089545da55b6 (#4151) - 6f1264f
Adds an initial integration test that:
1. captures laid-out widget size
2. focuses a text field to show the keyboard and resize the view
3. unfocuses the text field to dismiss the keyboard and resize the view
4. verify that the final widget size matches the initial size
