docs: Merge back from sprint repo Merge the result of the docs sprint back into master. Change-Id: I30161f4bfc30a14b2d55dae1bc13f5396217d6b7

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+# Android Log
+
+_This data source is supported only on Android userdebug builds._
+
+The "android.log" data source records log events from the Android log
+daemon (`logd`). These are the same log messages that are available via
+`adb logcat`.
+
+Both textual events and binary-formatted events from the [EventLog] are
+supported.
+
+This allows you to see log events time-synced with the rest of the trace. When recording
+[long traces](/docs/concepts/config#long-traces), it allows you to record event
+logs indefinitely, regardless of the Android log daemon buffer size
+(i.e. log events are periodically fetched and copied into the trace buffer).
+
+The data source can be configured to filter event from specific log buffers and
+keep only the events matching specific tags or priority.
+
+[EventLog]: https://developer.android.com/reference/android/util/EventLog
+
+### UI
+
+At the UI level, log events are showed in two widgets:
+
+1. A summary track that allows to quickly glance at the distribution of events
+   and their severity on the timeline.
+
+2. A table, time-synced with the viewport, that allows to see events within the
+   selected time range.
+
+![](/docs/images/android_logs.png "Android logs in the UI")
+
+### SQL
+
+```sql
+select l.ts, t.tid, p.pid, p.name as process, l.prio, l.tag, l.msg
+from android_logs as l left join thread as t using(utid) left join process as p using(upid)
+```
+ts | tid | pid | process | prio | tag | msg
+---|-----|-----|---------|------|-----|----
+291474737298264 | 29128 | 29128 | traced_probes | 4 | perfetto | probes_producer.cc:231 Ftrace setup (target_buf=1)
+291474852699265 | 625 | 625 | surfaceflinger | 3 | SurfaceFlinger | Finished setting power mode 1 on display 0
+291474853274109 | 1818 | 1228 | system_server | 3 | SurfaceControl | Excessive delay in setPowerMode()
+291474882474841 | 1292 | 1228 | system_server | 4 | DisplayPowerController | Unblocked screen on after 242 ms
+291474918246615 | 1279 |    1228 | system_server | 4 | am_pss | Pid=28568 UID=10194 Process Name="com.google.android.apps.fitness" Pss=12077056 Uss=10723328 SwapPss=183296 Rss=55021568 StatType=0 ProcState=18 TimeToCollect=51
+
+### TraceConfig
+
+Trace proto:
+[AndroidLogConfig](/docs/reference/trace-packet-proto.autogen#AndroidLogConfig)
+
+Config proto:
+[AndroidPowerConfig](/docs/reference/trace-config-proto.autogen#AndroidPowerConfig)
+
+Sample config:
+
+```protobuf
+data_sources: {
+    config {
+        name: "android.log"
+        android_log_config {
+            min_prio: PRIO_VERBOSE
+            filter_tags: "perfetto"
+            filter_tags: "my_tag_2"
+            log_ids: LID_DEFAULT
+            log_ids: LID_RADIO
+            log_ids: LID_EVENTS
+            log_ids: LID_SYSTEM
+            log_ids: LID_CRASH
+            log_ids: LID_KERNEL
+        }
+    }
+}
+```