Do not query CS in NetworkProvider constructor

ConnectivityService may not be available in a NetworkProvider
constructor, if it is created (but still unused) before
ConnectivityService starts.

As ConnectivityManager is only necessary in
declareNetworkRequestUnfulfillable, which should not be called often,
just query ConnectivityManager at that point.

This is necessary for VcnManagementService, which is started before
ConnectivityService and creates its NetworkProvider in its constructor.
Fortunately VcnManagementService does not call
declareNetworkRequestUnfulfillable at this point.

ConnectivityManager may be migrated to classic service getters that
cache "null" when the service was not available the first time it is
queried, so no system service must query it before it starts.

Bug: 171540887
Test: atest FrameworksNetTests:NetworkProviderTest
Change-Id: I8dadcd0e1360a9464192f330493e13aa69dd9fe2

tests/net/common/java/android/net/NetworkProviderTest.kt

@@ -33,6 +33,9 @@ import org.junit.After
 import org.junit.Before
 import org.junit.Test
 import org.junit.runner.RunWith
+import org.mockito.Mockito.doReturn
+import org.mockito.Mockito.mock
+import org.mockito.Mockito.verifyNoMoreInteractions
 import java.util.UUID
 import kotlin.test.assertEquals
 import kotlin.test.assertNotEquals
@@ -87,8 +90,8 @@ class NetworkProviderTest {
         ) = seenEvents.poll(DEFAULT_TIMEOUT_MS) { it is T && predicate(it) }
     }
 
-    private fun createNetworkProvider(): TestNetworkProvider {
-        return TestNetworkProvider(context, mHandlerThread.looper)
+    private fun createNetworkProvider(ctx: Context = context): TestNetworkProvider {
+        return TestNetworkProvider(ctx, mHandlerThread.looper)
     }
 
     @Test
@@ -169,7 +172,12 @@ class NetworkProviderTest {
 
     @Test
     fun testDeclareNetworkRequestUnfulfillable() {
-        val provider = createNetworkProvider()
+        val mockContext = mock(Context::class.java)
+        val provider = createNetworkProvider(mockContext)
+        // ConnectivityManager not required at creation time
+        verifyNoMoreInteractions(mockContext)
+        doReturn(mCm).`when`(mockContext).getSystemService(Context.CONNECTIVITY_SERVICE)
+
         mCm.registerNetworkProvider(provider)
 
         val specifier = StringNetworkSpecifier(UUID.randomUUID().toString())