Shorten the namespace and re-normalize include guards.

Change-Id: I93af4c1f19edf31098abd20ded1fcca6c5d83854
diff --git a/src/assembler_x86.h b/src/assembler_x86.h
index 05dfe31..c1c16c7 100644
--- a/src/assembler_x86.h
+++ b/src/assembler_x86.h
@@ -9,8 +9,7 @@
 #include "src/macros.h"
 #include "src/utils.h"
 
-namespace android {
-namespace runtime {
+namespace art {
 
 class Immediate {
  public:
@@ -474,6 +473,6 @@
   EmitUint8(0x66);
 }
 
-} }  // namespace android::runtime
+}  // namespace art
 
 #endif  // ART_SRC_ASSEMBLER_X86_H_