Define LMK reason metric

Only define the minimal proto and add a test.

Bug: 144281172
Change-Id: I4638e93ab13f6234be0eafd7022c6aed776244e2
diff --git a/BUILD b/BUILD
index f1dc21a..b843e81 100644
--- a/BUILD
+++ b/BUILD
@@ -586,6 +586,7 @@
         "src/trace_processor/metrics/android/android_cpu_agg.sql",
         "src/trace_processor/metrics/android/android_ion.sql",
         "src/trace_processor/metrics/android/android_lmk.sql",
+        "src/trace_processor/metrics/android/android_lmk_reason.sql",
         "src/trace_processor/metrics/android/android_mem.sql",
         "src/trace_processor/metrics/android/android_mem_unagg.sql",
         "src/trace_processor/metrics/android/android_package_list.sql",
@@ -1690,6 +1691,7 @@
         "protos/perfetto/metrics/android/ion_metric.proto",
         "protos/perfetto/metrics/android/java_heap_stats.proto",
         "protos/perfetto/metrics/android/lmk_metric.proto",
+        "protos/perfetto/metrics/android/lmk_reason_metric.proto",
         "protos/perfetto/metrics/android/mem_metric.proto",
         "protos/perfetto/metrics/android/mem_unagg_metric.proto",
         "protos/perfetto/metrics/android/package_list.proto",