Replace our home-grown BitCast with bit_cast from Chrome/Google3.

test/cctest/test-code-stubs.cc

 // Copyright 2013 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 44 matching lines @@
   uint32_t unsigned_exponent = static_cast<uint32_t>(exponent);
   int result = 0;
   uint32_t max_exponent =
     static_cast<uint32_t>(Double::kPhysicalSignificandSize);
   if (unsigned_exponent >= max_exponent) {
     if ((exponent - Double::kPhysicalSignificandSize) < 32) {
       result = dbl.u[0] << (exponent - Double::kPhysicalSignificandSize);
     }
   } else {
     uint64_t big_result =
-        (BitCast<uint64_t>(d) & Double::kSignificandMask) | Double::kHiddenBit;
+        (bit_cast<uint64_t>(d) & Double::kSignificandMask) | Double::kHiddenBit;
     big_result = big_result >> (Double::kPhysicalSignificandSize - exponent);
     result = static_cast<uint32_t>(big_result);
   }
   if (static_cast<int32_t>(exponent_bits) < 0) {
     return (0 - result);
   } else {
     return result;
   }
 }
 
@@ skipping 105 matching lines @@
 
 #define CHECK_STUB(NAME)                        \
   {                                             \
     HandleScope scope(isolate);                 \
     NAME##Stub stub_impl(0xabcd, isolate);      \
     CodeStub* stub = &stub_impl;                \
     CHECK_EQ(stub->MajorKey(), CodeStub::NAME); \
   }
   CODE_STUB_LIST(CHECK_STUB);
 }