[Docs] Move startup tracing docs into repository

components/tracing/docs/memory_infra_startup_tracing.md

+# Startup Tracing with MemoryInfra
+
+[MemoryInfra](memory_infra.md) supports startup tracing.
+
+## The Simple Way
+
+Start Chrome as follows:
+
+    $ chrome --no-sandbox \
+             --trace-startup=-*,disabled-by-default-memory-infra \
+             --trace-startup-file=/tmp/trace.json \
+             --trace-startup-duration=7
+
+This will use the default configuration: one memory dump every 250 ms with a
+detailed dump ever two seconds.
+
+## The Advanced Way
+
+If you need more control over the granularity of the memory dumps, you can
+specify a custom trace config file as follows:
+
+    $ cat > /tmp/trace.config
+    {
+      "startup_duration": 4,
+      "result_file": "/tmp/trace.json",
+      "trace_config": {
+        "included_categories": ["disabled-by-default-memory-infra"],
+        "excluded_categories": ["*"],
+        "memory_dump_config": {
+          "triggers": [
+            { "mode": "light", "periodic_interval_ms": 50 },
+            { "mode": "detailed", "periodic_interval_ms": 1000 }
+          ]
+        }
+      }
+    }
+
+    $ chrome --no-sandbox --trace-config-file=/tmp/trace.config
+
+## Related Pages
+
+ * [General information about startup tracing](https://sites.google.com/a/chromium.org/dev/developers/how-tos/trace-event-profiling-tool/recording-tracing-runs)
+ * [Memory tracing with MemoryInfra](memory_infra.md)