Enables ADBD tracing in emulator.

When running inside the emulator, guest's adbd can connect to 'adb-debug' qemud
service that can display adb trace messages on condition that emulator has been
started with '-debug adb' option.

This CL contains emulator code that enables that.

Change-Id: I6720deef0833fd02e2fe80deeaafbcf517de0c33
diff --git a/android/utils/debug.h b/android/utils/debug.h
index 272499a..ec3094d 100644
--- a/android/utils/debug.h
+++ b/android/utils/debug.h
@@ -41,6 +41,7 @@
     _VERBOSE_TAG(gles,         "hardware OpenGLES emulation") \
     _VERBOSE_TAG(adbserver,    "ADB server") \
     _VERBOSE_TAG(adbclient,    "ADB QEMU client") \
+    _VERBOSE_TAG(adb,          "ADB debugger") \
 
 #define  _VERBOSE_TAG(x,y)  VERBOSE_##x,
 typedef enum {