Add clear method to ProtoOutputStream so it is reusable by just
rewinding its internal pointer.

Bug: 72319159
Test: atest incidentd_test and atest statsd_test
Change-Id: Id046b987a7460d68300e5d4d46ae56aec1eba2d0
diff --git a/libs/protoutil/src/ProtoOutputStream.cpp b/libs/protoutil/src/ProtoOutputStream.cpp
index f24abae..9d9ffec 100644
--- a/libs/protoutil/src/ProtoOutputStream.cpp
+++ b/libs/protoutil/src/ProtoOutputStream.cpp
@@ -36,6 +36,18 @@
 {
 }
 
+
+void
+ProtoOutputStream::clear()
+{
+    mBuffer.clear();
+    mCopyBegin = 0;
+    mCompact = false;
+    mDepth = 0;
+    mObjectId = 0;
+    mExpectedObjectToken = 0LL;
+}
+
 bool
 ProtoOutputStream::write(uint64_t fieldId, double val)
 {