Extend MetricsFactory so it can log to different LogWriters

- Renamed MetricsFractory to MetricsFeatureProvider, and access it using
  FeatureFactory.
- Instead of containing exactly 1 logWriter, MetricsFeatureProvider now
  contain a list.
- Added OnAttach event in Lifecycle. This is needed when a mixin
  requires Context to initialize itself.
- Updated tests.

Bug: 29575437
Test: make RunSettingsRoboTests
Change-Id: I7cc1528b9a744cd40088701e2bd115f41a8bf744

src/com/android/settings/overlay/FeatureFactoryImpl.java

@@ -18,6 +18,9 @@ package com.android.settings.overlay;
 
 import android.content.Context;
 import android.support.annotation.Keep;
+
+import com.android.settings.core.instrumentation.MetricsFeatureProvider;
+import com.android.settings.core.instrumentation.MetricsFeatureProviderImpl;
 import com.android.settings.fuelgauge.PowerUsageFeatureProvider;
 
 /**
@@ -26,11 +29,21 @@ import com.android.settings.fuelgauge.PowerUsageFeatureProvider;
 @Keep
 public final class FeatureFactoryImpl extends FeatureFactory {
 
+    private MetricsFeatureProvider mMetricsFeatureProvider;
+
     @Override
     public SupportFeatureProvider getSupportFeatureProvider(Context context) {
         return null;
     }
 
+    @Override
+    public MetricsFeatureProvider getMetricsFeatureProvider() {
+        if (mMetricsFeatureProvider == null) {
+            mMetricsFeatureProvider = new MetricsFeatureProviderImpl();
+        }
+        return mMetricsFeatureProvider;
+    }
+
     @Override
     public PowerUsageFeatureProvider getPowerUsageFeatureProvider() {
         return null;