- added tools to help us document Flutter.framework for iOS
- filled in FlutterCodecs.h's missing documentation

* squashing the commits together

* directory rename, project rename. addressing reviewer comments

* update cirrus file

* change tool signature

* Add context ellipse polyfill
* Change call sites for ellipse
* Switch fontloader polyfill font for ie11

Co-authored-by: NAaron Clarke <aaclarke@google.com>

* fix shadows and mask filter blurs

* update goldens

* clarify the choice to min the shadows

Chrome Trace viewer treats events labeled "VSYNC" as special and highlights them (when the "Highlight Vsync" checkbox is enabled). Ideally VSYNC events are generated by the host system at their source. System VSYNC events are indeed present in full-system systraces. Flutter-level traces (as seen in Observatory/Flutter devtools) do not contain the system VSYNC events, so we rely on the engine to generate them (as close to where they would be generated by the system ideally).

Currently the common (platform-independent code) generates VSYNC events at the time when the UI thread starts processing a frame. This has two drawbacks:
1. The traces are generated with a delay (we wait for the callback to be have been scheduled on the UI thread instead of tracing as soon as the system notified us.
2. When inspecting system-wide traces we'll have both the system and the Flutter app (or potentially multiple Flutter apps) generate VSYNC events at the same time. This confuses both the developers and the trace viewer.

This change moves the VSYNC event generation to the platform-specific embedder implementations:
1. On Android/iOS we always generate the VSYNC event since Android/iOS developers use Flutter tools to debug the apps.
2. On Fuchsia we do not generate VSYNC events since the systraces always contain them.
3. In the Embedder wrapper we don not generate VSYNC events and rely on the actual embedder to do this in a way appropriate for the target system.

https://skia.googlesource.com/skia.git/+log/50d7d6fd7280..f6ed96d1c23b

git log 50d7d6fd7280..f6ed96d1c23b --date=short --first-parent --format='%ad %ae %s'
2020-03-05 egdaniel@google.com Revert "Move GrGpuResource GrSurface and GrTexture into src."
2020-03-05 mtklein@google.com add an ulp of error on the clamp asserts
2020-03-04 mtklein@google.com better SKVM_JIT_STATS output
2020-03-04 mtklein@google.com skip dump checks on machines w/o FMAs
2020-03-04 reed@google.com detect when the localmatrix forces us into a perspective stage
2020-03-04 egdaniel@google.com Move GrGpuResource GrSurface and GrTexture into src.
2020-03-04 mtklein@google.com async llvm compile, take 2
2020-03-04 mtklein@google.com turn off LLVM FMA discovery
2020-03-04 mtklein@google.com do our own fma discovery
2020-03-04 mtklein@google.com get rid of troublesome Op::round
2020-03-04 nifong@google.com Remove experimental from name of skm44 canvas methods

Created with:
  gclient setdep -r src/third_party/skia@f6ed96d1c23b

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/skia-flutter-autoroll
Please CC herb@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

Bug: None
Tbr: herb@google.com

On Linux, there is rarely just one default font that can reasonably be expected to be on the platform. This PR changes the GetDefaultFontFamily call to be GetDefaultFontFamilies, and it now returns a vector<string> so that the font collection code can look up all of them, and if any of them exist, add them to the fallback list.

For Linux, I supplied the list "Ubuntu", "Cantarell", "DejaVu Sans", "Liberation Sans", and "Arial", which should cover a large proportion of linux machines. For the other platforms, I supplied a list of length one, containing the one fallback font that used to be defined. On Windows, I added "Segoe UI" as a default, since that is the default system font on newer Windows.

The goal of this function is to provide at least one font family that is installed, since otherwise linux (or any platform) will just have no font at all if the default font isn't found.