atrace: introduce tracing category for adb.

Bug: http://b/31289465
Test: systrace
Change-Id: Ida5e898206e5b224771393d2d2ba609183dc3b90
diff --git a/cmds/atrace/atrace.cpp b/cmds/atrace/atrace.cpp
index f4c6be2..c176101 100644
--- a/cmds/atrace/atrace.cpp
+++ b/cmds/atrace/atrace.cpp
@@ -109,6 +109,7 @@
     { "ss",         "System Server",    ATRACE_TAG_SYSTEM_SERVER, { } },
     { "database",   "Database",         ATRACE_TAG_DATABASE, { } },
     { "network",    "Network",          ATRACE_TAG_NETWORK, { } },
+    { "adb",        "ADB",              ATRACE_TAG_ADB, { } },
     { k_coreServiceCategory, "Core services", 0, { } },
     { "sched",      "CPU Scheduling",   0, {
         { REQ,      "/sys/kernel/debug/tracing/events/sched/sched_switch/enable" },