Expand logging capabilities of Tethering subsystem

Introduce a SharedLog that can be shared among all Tethering
components.  All log entries go to the same log, and each includes
its subsystem name.  Additionally, all entries emitted to the
system log shared the same tag, so can easily be watched.

More subsystems can inherit a SharedLog, but to minimize cherry-pick
conflicts we limit ourselves to these changes only.

Test: as follows
    - built
    - flashed
    - booted
    - log output observed via dumpsys
    - runtest frameworks-net passes
Bug: 32163131
Bug: 36988090
Bug: 38218697
Change-Id: I1229d4c55987402d84b0d4a2c8a595e0c829aa3e
diff --git a/tests/net/java/com/android/server/connectivity/tethering/TetherInterfaceStateMachineTest.java b/tests/net/java/com/android/server/connectivity/tethering/TetherInterfaceStateMachineTest.java
index a3f33dc..27e683c 100644
--- a/tests/net/java/com/android/server/connectivity/tethering/TetherInterfaceStateMachineTest.java
+++ b/tests/net/java/com/android/server/connectivity/tethering/TetherInterfaceStateMachineTest.java
@@ -38,6 +38,7 @@
 import android.net.ConnectivityManager;
 import android.net.INetworkStatsService;
 import android.net.InterfaceConfiguration;
+import android.net.util.SharedLog;
 import android.os.INetworkManagementService;
 import android.os.RemoteException;
 import android.os.test.TestLooper;
@@ -63,12 +64,14 @@
     @Mock private IControlsTethering mTetherHelper;
     @Mock private InterfaceConfiguration mInterfaceConfiguration;
     @Mock private IPv6TetheringInterfaceServices mIPv6TetheringInterfaceServices;
+    @Mock private SharedLog mSharedLog;
 
     private final TestLooper mLooper = new TestLooper();
     private TetherInterfaceStateMachine mTestedSm;
 
     private void initStateMachine(int interfaceType) throws Exception {
-        mTestedSm = new TetherInterfaceStateMachine(IFACE_NAME, mLooper.getLooper(), interfaceType,
+        mTestedSm = new TetherInterfaceStateMachine(
+                IFACE_NAME, mLooper.getLooper(), interfaceType, mSharedLog,
                 mNMService, mStatsService, mTetherHelper, mIPv6TetheringInterfaceServices);
         mTestedSm.start();
         // Starting the state machine always puts us in a consistent state and notifies
@@ -90,12 +93,13 @@
 
     @Before public void setUp() throws Exception {
         MockitoAnnotations.initMocks(this);
+        when(mSharedLog.forSubComponent(anyString())).thenReturn(mSharedLog);
     }
 
     @Test
     public void startsOutAvailable() {
         mTestedSm = new TetherInterfaceStateMachine(IFACE_NAME, mLooper.getLooper(),
-                TETHERING_BLUETOOTH, mNMService, mStatsService, mTetherHelper,
+                TETHERING_BLUETOOTH, mSharedLog, mNMService, mStatsService, mTetherHelper,
                 mIPv6TetheringInterfaceServices);
         mTestedSm.start();
         mLooper.dispatchAll();