Changes since last roll:
```
ed303c628 Roll dart sdk again. Previous roll required 23ae4fa098 revert. (#4966)
8cd272733 Revert "Roll dart to 7764e6962e22afcf4b58c4e3cef3147330f3c884. (#4960)" (#4965)
9199b40f2 Revert "Support multiple shells in a single process. (#4932)" (#4964)
6baff4c82 Support multiple shells in a single process. (#4932)
31c5bb427 Roll dart to 7764e6962e22afcf4b58c4e3cef3147330f3c884. (#4960)
c8e4c6984 Avoid copying the contents of large platform message responses (#4947)
5ff527295 Update to use new vulkan GrBackendRenderTarget ctor. (#4962)
0c8993a1a Update to use new vulkan GrBackendRenderTarget ctor (part 2) (#4963)
132ebdda8 Revert "Roll src/third_party/skia/ 9874bf1bc..52e16d984 (135 commits) (#4958)" (#4961)
11882ab9e Roll src/third_party/skia/ 9874bf1bc..52e16d984 (135 commits) (#4958)
```
Add consts
This reverts commit 67cf7918cf.
Reverting because this causes scuba regressions that I'd like to
address in another PR that is pending, but we'd like to roll Flutter.
Fixes InputDecorator to work with textScaleFactor, fixes Material Design differences.
There were a number of differences with the Material Design spec, including
several different padding values and underline thickness. This corrects
that so that the decorator is in line with the Material Design spec now.
Also, the decorator properly handles changes to the textScaleFactor, where
before it would not re-layout when needed, painting the cursor and
underline incorrectly.
The decorator also now properly animates helper, error, and hint text when
the textScaleFactor or input decoration properties change.
Helper text is now properly displayed in dense mode, as the spec shows.
Before this change, it was never displayed in dense mode.
Fixes#12485
