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

src/x64/builtins-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 10 matching lines @@
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // 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 "codegen-inl.h"
 
-namespace v8 { namespace internal {
+namespace v8 {
+namespace internal {
 
 void Builtins::Generate_Adaptor(MacroAssembler* masm,
                                 Builtins::CFunctionId id) {
   masm->int3();  // UNIMPLEMENTED.
 }
 
 void Builtins::Generate_ArgumentsAdaptorTrampoline(MacroAssembler* masm) {
   masm->int3();  // UNIMPLEMENTED.
 }
 
@@ skipping 13 matching lines @@
   masm->int3();  // UNIMPLEMENTED.
 }
 
 void Builtins::Generate_JSEntryTrampoline(MacroAssembler* masm) {
   masm->int3();  // UNIMPLEMENTED.
 }
 
 } }  // namespace v8::internal