Fix rounding in Uint8ClampedArray setter.

src/platform.h

Index: src/platform.h
diff --git a/src/platform.h b/src/platform.h
index 14f4551f372e2c5faed9e9f8312ad1ab84a0c519..7a32229b5bc6b506e0149c82927bad438232c6f5 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -71,6 +71,24 @@ int signbit(double x);
 
 int strncasecmp(const char* s1, const char* s2, int n);
 
+inline int lrint(double flt) {
+  int intgr;
+#if defined(V8_TARGET_ARCH_IA32)
+  __asm {
+    fld flt
+    fistp intgr
+  };
+#else
+  intgr = static_cast<int>(flt + 0.5);
+  if ((intgr & 1) != 0 && intgr - flt == 0.5) {
+    // If the number is halfway between two integers, round to the even one.
+    intgr--;
+  }
+  return intgr;
+#endif
+}
+
+
 #endif  // _MSC_VER
 
 // Random is missing on both Visual Studio and MinGW.