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/Thumb2/Ralloc.cc b/src/compiler/codegen/arm/Thumb2/Ralloc.cc
index 63d2430..59c1aa6 100644
--- a/src/compiler/codegen/arm/Thumb2/Ralloc.cc
+++ b/src/compiler/codegen/arm/Thumb2/Ralloc.cc
@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+namespace art {
+
 /*
  * This file contains codegen for the Thumb ISA and is intended to be
  * includes by:
@@ -49,3 +51,5 @@
         return oatAllocTempFloat(cUnit);
     return oatAllocTemp(cUnit);
 }
+
+}  // namespace art