Reapply r5603 with additional fix: use OS::StrNCpy instead of posix strncpy.

src/conversions.cc

Index: src/conversions.cc
diff --git a/src/conversions.cc b/src/conversions.cc
index d4180640518279db9a19ab9580f6d15b5800cb80..a7a0867663926d7cb9c32366c39e58f94350ae2b 100644
--- a/src/conversions.cc
+++ b/src/conversions.cc
@@ -354,7 +354,7 @@ static double InternalStringToInt(Iterator current, EndMark end, int radix) {
     ASSERT(buffer_pos < kBufferSize);
     buffer[buffer_pos] = '\0';
     Vector<char> buffer_vector(buffer, buffer_pos);
-    return sign ? -strtod(buffer_vector, NULL) : strtod(buffer_vector, NULL);
+    return sign ? -Strtod(buffer_vector, 0) : Strtod(buffer_vector, 0);
   }
 
   // The following code causes accumulating rounding error for numbers greater
@@ -653,7 +653,7 @@ static double InternalStringToDouble(Iterator current,
   ASSERT(buffer_pos < kBufferSize);
   buffer[buffer_pos] = '\0';
 
-  double converted = strtod(Vector<char>(buffer, buffer_pos), exponent);
+  double converted = Strtod(Vector<char>(buffer, buffer_pos), exponent);
   return sign? -converted: converted;
 }