Document that ActionAnalysisMetadata#getOwner() is never null, add some Preconditions checks to make that more clear, and ensure that ActionOwner's fields are never null except for the SYSTEM_ACTION_OWNER wart.

Also do some drive-by serialization annotation clean-ups and other housekeeping.

PiperOrigin-RevId: 312336006
diff --git a/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteExecutionClientTest.java b/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteExecutionClientTest.java
index eec57b5..ef2e9c4 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteExecutionClientTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/GrpcRemoteExecutionClientTest.java
@@ -184,7 +184,7 @@
     fakeFileCache = new FakeActionInputFileCache(execRoot);
     simpleSpawn =
         new SimpleSpawn(
-            new FakeOwner("Mnemonic", "Progress Message"),
+            new FakeOwner("Mnemonic", "Progress Message", "//dummy:label"),
             ImmutableList.of("/bin/echo", "Hi!"),
             ImmutableMap.of("VARIABLE", "value"),
             /*executionInfo=*/ ImmutableMap.<String, String>of(),
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 9ff5ef9..2ab08c1 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
@@ -219,7 +219,7 @@
   private static SimpleSpawn simpleSpawnWithExecutionInfo(
       ImmutableMap<String, String> executionInfo) {
     return new SimpleSpawn(
-        new FakeOwner("Mnemonic", "Progress Message"),
+        new FakeOwner("Mnemonic", "Progress Message", "//dummy:label"),
         ImmutableList.of("/bin/echo", "Hi!"),
         ImmutableMap.of("VARIABLE", "value"),
         executionInfo,
diff --git a/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java b/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java
index a5b204b..030efa3 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/RemoteSpawnRunnerTest.java
@@ -844,7 +844,7 @@
             PathFragment.create("out/param_file"), args, ParameterFileType.UNQUOTED, ISO_8859_1);
     Spawn spawn =
         new SimpleSpawn(
-            new FakeOwner("foo", "bar"),
+            new FakeOwner("foo", "bar", "//dummy:label"),
             /*arguments=*/ ImmutableList.of(),
             /*environment=*/ ImmutableMap.of(),
             /*executionInfo=*/ ImmutableMap.of(),
@@ -1028,7 +1028,7 @@
   private static SimpleSpawn simpleSpawnWithExecutionInfo(
       ImmutableMap<String, String> executionInfo, Artifact... outputs) {
     return new SimpleSpawn(
-        new FakeOwner("foo", "bar"),
+        new FakeOwner("foo", "bar", "//dummy:label"),
         /*arguments=*/ ImmutableList.of(),
         /*environment=*/ ImmutableMap.of(),
         /*executionInfo=*/ executionInfo,