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/graph_visualizer.h b/compiler/optimizing/graph_visualizer.h
index ec636d8..66588f6 100644
--- a/compiler/optimizing/graph_visualizer.h
+++ b/compiler/optimizing/graph_visualizer.h
@@ -21,10 +21,9 @@
 
 #include "arch/instruction_set.h"
 #include "base/arena_containers.h"
-#include "base/macros.h"
 #include "base/value_object.h"
 
-namespace art HIDDEN {
+namespace art {
 
 class CodeGenerator;
 class DexCompilationUnit;