base: support logging before enter main function.

Bug: http://b/30974760
Test: run libbase_test.

Change-Id: I3f45fc21e8fe6301b5fef027728ea91f2188911d
diff --git a/base/logging_test.cpp b/base/logging_test.cpp
index 2d9c2ba..adb041b 100644
--- a/base/logging_test.cpp
+++ b/base/logging_test.cpp
@@ -594,3 +594,7 @@
 
   EXPECT_EQ(CountLineAborter::newline_count, 1U + 1U);  // +1 for final '\n'.
 }
+
+__attribute__((constructor)) void TestLoggingInConstructor() {
+  LOG(ERROR) << "foobar";
+}