Add generic layer metadata to Composer 2.4

Bug: 139747351
Test: VtsHalGraphicsComposerV2_4TargetTest
Test: Manual verification with a modified Composer implementation
Change-Id: I800841ab1348a93c73c25c5f8bcf2254d9dc22e8
diff --git a/graphics/composer/2.4/utils/vts/ComposerVts.cpp b/graphics/composer/2.4/utils/vts/ComposerVts.cpp
index 8a9c006..8cdc452 100644
--- a/graphics/composer/2.4/utils/vts/ComposerVts.cpp
+++ b/graphics/composer/2.4/utils/vts/ComposerVts.cpp
@@ -129,6 +129,16 @@
     return mClient->setContentType(display, contentType);
 }
 
+Error ComposerClient::getLayerGenericMetadataKeys(
+        std::vector<IComposerClient::LayerGenericMetadataKey>* outKeys) {
+    Error error = Error::NONE;
+    mClient->getLayerGenericMetadataKeys([&](const auto tmpError, const auto& tmpKeys) {
+        error = tmpError;
+        *outKeys = tmpKeys;
+    });
+    return error;
+}
+
 }  // namespace vts
 }  // namespace V2_4
 }  // namespace composer