The engine was using a global to store a timestamp representing the
launch of the engine. This timestamp is initialized with a JNI call
on Android and during shell setup on other platforms. Later the
timestamp is added to a FlutterEngineMainEnter timeline event used to
measure engine startup time in benchmarks.
This PR removes the global and the JNI call and moves the timestamp
into the settings object.
The BaseInputConnection superclass does not call endBatchEdit
in setSelection and therefore does not implicitly cause
InputConnectionAdaptor to send a state update.
Some input modes such as numeric keypads will not function without
these updates.
This PR touches variable names, class names, and file names so it's significantly more risky than its predecessor https://github.com/flutter/engine/pull/17329
Due to file name changes, this PR is expected to change the license files.
We haven't rename `shell/gpu` to `shell/raster` yet. It should be optional but I think it's better to have `raster_surface_software.cc` than `gpu_surface_software.cc`.
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.
