Extract hardcoded error strings into a single place and replace them with enum.

src/x64/codegen-x64.cc

 // Copyright 2012 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 376 matching lines @@
   __ JumpIfNotSmi(rbx, &convert_hole);
   __ SmiToInteger32(rbx, rbx);
   __ cvtlsi2sd(xmm0, rbx);
   __ movsd(FieldOperand(r14, r9, times_8, FixedDoubleArray::kHeaderSize),
            xmm0);
   __ jmp(&entry);
   __ bind(&convert_hole);
 
   if (FLAG_debug_code) {
     __ CompareRoot(rbx, Heap::kTheHoleValueRootIndex);
-    __ Assert(equal, "object found in smi-only array");
+    __ Assert(equal, kObjectFoundInSmiOnlyArray);
   }
 
   __ movq(FieldOperand(r14, r9, times_8, FixedDoubleArray::kHeaderSize), r15);
   __ bind(&entry);
   __ decq(r9);
   __ j(not_sign, &loop);
 
   __ bind(&done);
 }
 
@@ skipping 162 matching lines @@
   STATIC_ASSERT(kSeqStringTag == 0);
   __ testb(result, Immediate(kStringRepresentationMask));
   __ j(zero, &seq_string, Label::kNear);
 
   // Handle external strings.
   Label ascii_external, done;
   if (FLAG_debug_code) {
     // Assert that we do not have a cons or slice (indirect strings) here.
     // Sequential strings have already been ruled out.
     __ testb(result, Immediate(kIsIndirectStringMask));
-    __ Assert(zero, "external string expected, but not found");
+    __ Assert(zero, kExternalStringExpectedButNotFound);
   }
   // Rule out short external strings.
   STATIC_CHECK(kShortExternalStringTag != 0);
   __ testb(result, Immediate(kShortExternalStringTag));
   __ j(not_zero, call_runtime);
   // Check encoding.
   STATIC_ASSERT(kTwoByteStringTag == 0);
   __ testb(result, Immediate(kStringEncodingMask));
   __ movq(result, FieldOperand(string, ExternalString::kResourceDataOffset));
   __ j(not_equal, &ascii_external, Label::kNear);
@@ skipping 149 matching lines @@
          i++) {
       patcher.masm()->nop();
     }
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64