Add trace category for adb.

Bug: http://b/31289465
Test: systrace
Change-Id: I765c55c264329227556ff25655e3f00c5c3e8b54

core/java/android/os/Trace.java

@@ -83,6 +83,8 @@ public final class Trace {
     public static final long TRACE_TAG_DATABASE = 1L << 20;
     /** @hide */
     public static final long TRACE_TAG_NETWORK = 1L << 21;
+    /** @hide */
+    public static final long TRACE_TAG_ADB = 1L << 22;
 
     private static final long TRACE_TAG_NOT_READY = 1L << 63;
     private static final int MAX_SECTION_NAME_LEN = 127;