liblog: add log/log_time.h

Move log_time definitions to their own home.

struct log_time

Test: gTest liblog-unit-tests --gtest_filter=liblog.log_time
Bug: 34250038
Change-Id: I400cf4cc865d1c167699a4654ecb69455a18e604
diff --git a/liblog/tests/Android.mk b/liblog/tests/Android.mk
index 7bbf86d..8450675 100644
--- a/liblog/tests/Android.mk
+++ b/liblog/tests/Android.mk
@@ -58,7 +58,8 @@
     liblog_test.cpp \
     log_id_test.cpp \
     log_radio_test.cpp \
-    log_system_test.cpp
+    log_system_test.cpp \
+    log_time_test.cpp
 
 # to prevent breaking the build if bionic not relatively visible to us
 ifneq ($(wildcard $(LOCAL_PATH)/../../../../bionic/libc/bionic/libc_logging.cpp),)