Fuchsia: Hello, Fuchsia!

runtime/platform/utils_fuchsia.h

Index: runtime/platform/utils_fuchsia.h
diff --git a/runtime/platform/utils_fuchsia.h b/runtime/platform/utils_fuchsia.h
index 705422587974855b16149d441460869dd6b08558..a44fcb8b4869e17a43485bf5671cfbece9343122 100644
--- a/runtime/platform/utils_fuchsia.h
+++ b/runtime/platform/utils_fuchsia.h
@@ -10,14 +10,24 @@
 namespace dart {
 
 inline int Utils::CountLeadingZeros(uword x) {
-  UNIMPLEMENTED();
-  return 0;
+#if defined(ARCH_IS_32_BIT)
+  return __builtin_clzl(x);
+#elif defined(ARCH_IS_64_BIT)
+  return __builtin_clzll(x);
+#else
+#error Architecture is not 32-bit or 64-bit.
+#endif
 }
 
 
 inline int Utils::CountTrailingZeros(uword x) {
-  UNIMPLEMENTED();
-  return 0;
+#if defined(ARCH_IS_32_BIT)
+  return __builtin_ctzl(x);
+#elif defined(ARCH_IS_64_BIT)
+  return __builtin_ctzll(x);
+#else
+#error Architecture is not 32-bit or 64-bit.
+#endif
 }