X64: Convert doubles to int32 inline (without calling runtime).

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index adc136a7f8506e411ad260df2481a983d7d69df8..411a5b855983f333706d34e1e9e49ae0b6c51bcb 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -520,6 +520,16 @@ class MacroAssembler: public Assembler {
   // occurred.
   void IllegalOperation(int num_arguments);
 
+
+  // Converts a double precission floating point number to a 32-bit
+  // integer. It is equivalent to first converting the double to an
+  // integer by truncation (dropping decimals) and then finding the
+  // remainder modulo 2^32 of the result. Non-numbers like infinites
+  // and NaN are converted to zero.
+  // Uses rcx register as well, and dst can be same register as scratch,
+  // or same register as src, but src and scracth cannot be the same.
+  void DoubleToInteger32(Register dst, Register src, Register scratch);
+
   // ---------------------------------------------------------------------------
   // Runtime calls