Shorten the namespace and re-normalize include guards.

Change-Id: I93af4c1f19edf31098abd20ded1fcca6c5d83854
diff --git a/src/assembler_x86.cc b/src/assembler_x86.cc
index de2219c..ce7f104 100644
--- a/src/assembler_x86.cc
+++ b/src/assembler_x86.cc
@@ -7,8 +7,7 @@
 #include "src/assembler.h"
 #include "src/memory_region.h"
 
-namespace android {
-namespace runtime {
+namespace art {
 
 class DirectCallRelocation : public AssemblerFixup {
  public:
@@ -1347,4 +1346,4 @@
   EmitOperand(rm, Operand(operand));
 }
 
-} }  // namespace android::runtime
+} // namespace art