metrics: Implement getting prototext formatted metric result

Uses protozero_to_text to convert the metric proto result into
prototext, which will be used by the UI in a later CL.

Bug:161699653
Change-Id: I5cb9e3021855e6a71f756db3a3a77b6ff73346c5
diff --git a/Android.bp b/Android.bp
index 995769c..ab70cd7 100644
--- a/Android.bp
+++ b/Android.bp
@@ -8319,6 +8319,7 @@
     ":perfetto_src_trace_processor_track_event_descriptor",
     ":perfetto_src_trace_processor_types_types",
     ":perfetto_src_trace_processor_util_descriptors",
+    ":perfetto_src_trace_processor_util_protozero_to_text",
     ":perfetto_src_trace_processor_util_util",
     "src/trace_processor/trace_processor_shell.cc",
     "src/trace_processor/util/proto_to_json.cc",
@@ -8452,6 +8453,7 @@
     ":perfetto_src_trace_processor_track_event_descriptor",
     ":perfetto_src_trace_processor_types_types",
     ":perfetto_src_trace_processor_util_descriptors",
+    ":perfetto_src_trace_processor_util_protozero_to_text",
     ":perfetto_src_trace_processor_util_util",
     ":perfetto_tools_trace_to_text_common",
     ":perfetto_tools_trace_to_text_full",