logd: make LogBuffer an interface

We may use different implementations of LogBuffer in the future, so we
make it interface and create a concrete ChattyLogBuffer class that
implements it.

Test: logging unit tests
Change-Id: I5731d6404640664c9acc26b7c677dff3110c6a11
diff --git a/logd/LogReaderThread.cpp b/logd/LogReaderThread.cpp
index 4889c24..e58e3eb 100644
--- a/logd/LogReaderThread.cpp
+++ b/logd/LogReaderThread.cpp
@@ -84,13 +84,13 @@
         lock.unlock();
 
         if (tail_) {
-            logbuf.flushTo(client, start, nullptr, privileged_, can_read_security_logs_,
+            logbuf.FlushTo(client, start, nullptr, privileged_, can_read_security_logs_,
                            std::bind(&LogReaderThread::FilterFirstPass, this, _1));
             leading_dropped_ =
                     true;  // TODO: Likely a bug, if leading_dropped_ was not true before calling
                            // flushTo(), then it should not be reset to true after.
         }
-        start = logbuf.flushTo(client, start, last_tid_, privileged_, can_read_security_logs_,
+        start = logbuf.FlushTo(client, start, last_tid_, privileged_, can_read_security_logs_,
                                std::bind(&LogReaderThread::FilterSecondPass, this, _1));
 
         // We only ignore entries before the original start time for the first flushTo(), if we