Revert "Make compiler/optimizing/ symbols hidden."

This reverts commit e2727154f25e0db9a5bb92af494d8e47b181dfcf.

Reason for revert: Breaks ASAN tests (ODR violation).
Bug: 142365358

Change-Id: I38103d74a1297256c81d90872b6902ff1e9ef7a4
diff --git a/compiler/optimizing/common_dominator.h b/compiler/optimizing/common_dominator.h
index f01270e..9f012cf 100644
--- a/compiler/optimizing/common_dominator.h
+++ b/compiler/optimizing/common_dominator.h
@@ -17,10 +17,9 @@
 #ifndef ART_COMPILER_OPTIMIZING_COMMON_DOMINATOR_H_
 #define ART_COMPILER_OPTIMIZING_COMMON_DOMINATOR_H_
 
-#include "base/macros.h"
 #include "nodes.h"
 
-namespace art HIDDEN {
+namespace art {
 
 // Helper class for finding common dominators of two or more blocks in a graph.
 // The domination information of a graph must not be modified while there is