Shorten the namespace and re-normalize include guards.

Change-Id: I93af4c1f19edf31098abd20ded1fcca6c5d83854
diff --git a/src/assembler.h b/src/assembler.h
index d211b6f..228612e 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -7,8 +7,7 @@
 #include "src/macros.h"
 #include "src/memory_region.h"
 
-namespace android {
-namespace runtime {
+namespace art {
 
 class Assembler;
 class AssemblerBuffer;
@@ -227,7 +226,7 @@
   friend class AssemblerFixup;
 };
 
-} }  // namespace android::runtime
+}  // namespace art
 
 #if defined(__i386__)
 #include "src/assembler_x86.h"