Get the instance count as the initial value

Developer may not be able to enable strict mode before creating any
activities. The initial value of expected instance count may not always
be 1.

This CL use the instance count from InstanceTracker as the initial
value.

Bug: 152348723
Test: atest ActivityLeakTests
      atest NexusLauncherTests
Change-Id: I8d34c87748deac72cf8b6e5cc247029901bbffb3

core/java/android/os/StrictMode.java

@@ -817,6 +817,9 @@ public final class StrictMode {
 
             /** @hide */
             public @NonNull Builder permitActivityLeaks() {
+                synchronized (StrictMode.class) {
+                    sExpectedActivityInstanceCount.clear();
+                }
                 return disable(DETECT_VM_ACTIVITY_LEAKS);
             }
 
@@ -2586,8 +2589,10 @@ public final class StrictMode {
                 return;
             }
 
+            // Use the instance count from InstanceTracker as initial value.
             Integer expected = sExpectedActivityInstanceCount.get(klass);
-            Integer newExpected = expected == null ? 1 : expected + 1;
+            Integer newExpected =
+                    expected == null ? InstanceTracker.getInstanceCount(klass) + 1 : expected + 1;
             sExpectedActivityInstanceCount.put(klass, newExpected);
         }
     }