Trace-based benchmarking via a mojo app.

apps/benchmark/README.md

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+# benchmark
+
+This application connects to another mojo application, collects traces during
+indicated period of time and computes a number of results based on the collected
+traces. It can be used to measure performance of a mojo app, provided that the
+app being benchmarked participates in the [tracing
+ecosystem](mojo/services/tracing/public/interfaces/tracing.mojom).
+
+## Arguments
+
+The benchmarking app expects the following arguments:
+
+ - `--app=<app_url>` - url of the application to be benchmarked
+ - `--duration=<duration_seconds>` - duration of the benchmark in seconds
+
+any other arguments are assumed to be descriptions of measurements to be
+conducted on the collected trace data. Each measurement has to be of form:
+`<measurement_type>/<trace_event_category>/<trace_event_name>`.
+
+The following measurement types are available:
+
+ - `time_until` - measures time until the first occurence of the event named
+   `trace_event_name` in category `trace_event_category`.
+ - `avg_duration` - measures average duration of all events named
+   `trace_event_name` in category `trace_event_category`.
+
+## Runner script
+
+Devtools offers [a helper script](mojo/devtools/common/mojo_benchmark) allowing
+to run a list of benchmarks, including on an Android device.