Propagating whether there was a cache hit in the SpawnResult.

So far, nobody uses it, but I want to start using this field soon.

TESTED=unit test
RELNOTES: None
PiperOrigin-RevId: 186290375
diff --git a/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnCacheTest.java b/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnCacheTest.java
index 3e8bb83..4ed3dafb 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnCacheTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnCacheTest.java
@@ -236,6 +236,7 @@
             any(Boolean.class));
     assertThat(result.setupSuccess()).isTrue();
     assertThat(result.exitCode()).isEqualTo(0);
+    assertThat(result.isCacheHit()).isTrue();
     // We expect the CachedLocalSpawnRunner to _not_ write to outErr at all.
     assertThat(outErr.hasRecordedOutput()).isFalse();
     assertThat(outErr.hasRecordedStderr()).isFalse();