Avoid inopportune GC with explicit gc() call

Bug: 207077101

Test: Treehugger
Change-Id: If9d01f6069a340b94b3703177bf4db51e10d975d
diff --git a/tools/ahat/src/test-dump/Main.java b/tools/ahat/src/test-dump/Main.java
index 2e29076..711d662 100644
--- a/tools/ahat/src/test-dump/Main.java
+++ b/tools/ahat/src/test-dump/Main.java
@@ -43,6 +43,10 @@
     // Allocate the instance of DumpedStuff.
     stuff = new DumpedStuff(baseline);
 
+    // Preemptively garbage collect to avoid an inopportune GC triggering
+    // after this.
+    Runtime.getRuntime().gc();
+
     // Create a bunch of unreachable objects pointing to basicString for the
     // reverseReferencesAreNotUnreachable test
     for (int i = 0; i < 100; i++) {
diff --git a/tools/ahat/src/test/com/android/ahat/InstanceTest.java b/tools/ahat/src/test/com/android/ahat/InstanceTest.java
index 376122b..1f29030 100644
--- a/tools/ahat/src/test/com/android/ahat/InstanceTest.java
+++ b/tools/ahat/src/test/com/android/ahat/InstanceTest.java
@@ -224,6 +224,7 @@
   @Test
   public void reachability() throws IOException {
     TestDump dump = TestDump.getTestDump();
+    // We were careful to avoid GC before dumping, so nothing here should be null.
     AhatInstance strong1 = dump.getDumpedAhatInstance("reachabilityReferenceChain");
     AhatInstance soft1 = strong1.getField("referent").asAhatInstance();
     AhatInstance strong2 = soft1.getField("referent").asAhatInstance();