Fix bug in x64 RegExp detecting start of string.

src/regexp-macro-assembler-tracer.cc

Index: src/regexp-macro-assembler-tracer.cc
diff --git a/src/regexp-macro-assembler-tracer.cc b/src/regexp-macro-assembler-tracer.cc
index b32d71dba5aca3a57a295944e14cece01be25420..0a638e73204f5e59e689fb276ae2628c478405bd 100644
--- a/src/regexp-macro-assembler-tracer.cc
+++ b/src/regexp-macro-assembler-tracer.cc
@@ -37,8 +37,8 @@ RegExpMacroAssemblerTracer::RegExpMacroAssemblerTracer(
     RegExpMacroAssembler* assembler) :
   assembler_(assembler) {
   unsigned int type = assembler->Implementation();
-  ASSERT(type < 4);
-  const char* impl_names[4] = {"IA32", "ARM", "X64", "Bytecode"};
+  ASSERT(type < 5);
+  const char* impl_names[4] = {"IA32", "ARM", "MIPS", "X64", "Bytecode"};
   PrintF("RegExpMacroAssembler%s();\n", impl_names[type]);
 }