[docs] Document MemoryInfra startup tracing on Android

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
 
+On Android, enable startup tracing and start Chrome as follows:
+
+    $ build/android/adb_chrome_public_command_line \
+          --no-sandbox \

[Primiano Tucci (use gerrit), 2016/02/11 12:04:55]

no need of --no-sandbox on Android.
Let's keep the one above for a bit, until it makes to stable. IIRC on Android we
never really needed no-sanbox, was a linux thing only.

[petrcermak, 2016/02/11 12:20:49]

Done.

+          --trace-startup=-*,disabled-by-default-memory-infra \
+          --trace-startup-file=/storage/emulated/legacy/Download/trace.json \
+          --trace-startup-duration=7
+
+    $ build/android/adb_run_chrome_public  # Public.
+    $ clank/bin/adb_run_chrome             # Googlers only.

[Primiano Tucci (use gerrit), 2016/02/11 12:04:55]

hmm remove this, I imagine internal folks know how do run chrome.
Also because otherwise you need a copy also of the command line command above

+
+    $ adb pull /storage/emulated/legacy/Download/trace.json  # After tracing.

[Primiano Tucci (use gerrit), 2016/02/11 12:04:55]

I think that this should be aliased also via /sdcard/Download/trace.json, which
is easier to type and remember

[petrcermak, 2016/02/11 12:20:49]

Done (I wanted to mirror
https://www.chromium.org/developers/how-tos/trace-event-profiling-tool/record...,
which mentions both).

+
 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
 
+On Android, the config file has to be pushed to a fixed file location:
+
+    $ adb root
+    $ adb push /tmp/trace.config /data/local/chrome-trace-config.json
+
+    $ build/android/adb_chrome_public_command_line --no-sandbox

[Primiano Tucci (use gerrit), 2016/02/11 12:04:55]

no need of --no-sandbox

[petrcermak, 2016/02/11 12:20:49]

Done.

+
+    $ build/android/adb_run_chrome_public  # Public.
+    $ clank/bin/adb_run_chrome             # Googlers only.

[Primiano Tucci (use gerrit), 2016/02/11 12:04:55]

ditto

[petrcermak, 2016/02/11 12:20:49]

Done (ditto).

+
+    $ adb pull /storage/emulated/legacy/Download/trace.json  # After tracing.
+
+Make sure that the "result_file" location is writable by the Chrome process on
+Android (e.g. "/storage/emulated/legacy/Download/trace.json"). Note that startup

[Primiano Tucci (use gerrit), 2016/02/11 12:04:55]

/sdcard

[petrcermak, 2016/02/11 12:20:49]

Done.

+tracing will be enabled upon every Chrome launch until you delete the config
+file:
+
+    $ adb shell rm /data/local/chrome-trace-config.json
+
 ## 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)