Split nested namespaces declaration in two lines in accordance with C++ Style Guide.

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index d6d66d3665ae895986221bd1e7d0dc5a37d3947b..9ee6f666c84718ba5d73cff7cca3f578f6991c37 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -29,7 +29,8 @@
 
 #include "macro-assembler.h"
 
-namespace v8 { namespace internal {
+namespace v8 {
+namespace internal {
 
 Register no_reg = { -1 };
 
@@ -318,7 +319,8 @@ void Assembler::mov(Register dst, Register src) {
 #include "stub-cache.h"
 #include "unicode.h"
 
-namespace v8 { namespace internal {
+namespace v8 {
+namespace internal {
 
 void ArgumentsAccessStub::GenerateNewObject(MacroAssembler* a) {
   UNIMPLEMENTED();