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

src/x64/macro-assembler-x64.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 12 matching lines @@
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "v8.h"
 
 #include "bootstrapper.h"
 #include "codegen-inl.h"
 
-namespace v8 { namespace internal {
+namespace v8 {
+namespace internal {
 
 MacroAssembler::MacroAssembler(void* buffer, int size)
   : Assembler(buffer, size),
     unresolved_(0),
     generating_stub_(false),
     allow_stub_calls_(true),
     code_object_(Heap::undefined_value()) {
 }
 
 void MacroAssembler::TailCallRuntime(ExternalReference const& a, int b) {
   UNIMPLEMENTED();
 }
 
 } }  // namespace v8::internal