Reduce namespace pollution.

This leaves us with just the mspace stuff and three libdex functions to clean
up. We deliberately expose the JII API, and I don't think there's anything we
can really do about the art_..._from_code stuff (and at least that starts with
"art_").

Change-Id: I77e58e8330cd2afeb496642302dfe3311e68091a
diff --git a/src/compiler/codegen/arm/Assemble.cc b/src/compiler/codegen/arm/Assemble.cc
index a73a27a..83c7a6c 100644
--- a/src/compiler/codegen/arm/Assemble.cc
+++ b/src/compiler/codegen/arm/Assemble.cc
@@ -20,6 +20,8 @@
 #include "Codegen.h"
 #include <sys/mman.h>           /* for protection change */
 
+namespace art {
+
 #define MAX_ASSEMBLER_RETRIES 50
 
 /*
@@ -1594,3 +1596,5 @@
      */
     createMappingTable(cUnit);
 }
+
+}  // namespace art