Move LogHistogram out of heapprofd_producer.

The file is getting very long.

Change-Id: I114d9aa17c443dd0c9908a3924bfa600d8669a3e
diff --git a/Android.bp b/Android.bp
index 68061d4..ea75b19 100644
--- a/Android.bp
+++ b/Android.bp
@@ -6816,6 +6816,7 @@
     "src/profiling/memory/bookkeeping_dump.cc",
     "src/profiling/memory/heapprofd_producer.cc",
     "src/profiling/memory/java_hprof_producer.cc",
+    "src/profiling/memory/log_histogram.cc",
     "src/profiling/memory/system_property.cc",
     "src/profiling/memory/unwinding.cc",
   ],