logd: add a SerializedLogBuffer suitable for compression

Initial commit for a SerializedLogBuffer.  The intention here is for
the serialized data to be compressed (currently using zlib) to allow
for substantially longer logs in the same memory footprint.

Test: unit tests
Change-Id: I2528e4e1ff1cf3bc91130173a107f371f04d911a
diff --git a/logd/LogBufferTest.cpp b/logd/LogBufferTest.cpp
index 412b6f1..47d2a2f 100644
--- a/logd/LogBufferTest.cpp
+++ b/logd/LogBufferTest.cpp
@@ -455,4 +455,5 @@
     CompareLogMessages(after_clear_messages, read_log_messages_after_clear);
 }
 
-INSTANTIATE_TEST_CASE_P(LogBufferTests, LogBufferTest, testing::Values("chatty", "simple"));
+INSTANTIATE_TEST_CASE_P(LogBufferTests, LogBufferTest,
+                        testing::Values("chatty", "serialized", "simple"));