Add Smi::Zero and replace all Smi::FromInt(0) calls

test/cctest/test-api.cc

Index: test/cctest/test-api.cc
diff --git a/test/cctest/test-api.cc b/test/cctest/test-api.cc
index 8317a06aa22b5bad9e35296ae02037cef0e44d54..c72f6f6b405599e3170b93b21c7cae1768027d6c 100644
--- a/test/cctest/test-api.cc
+++ b/test/cctest/test-api.cc
@@ -151,6 +151,8 @@ UNINITIALIZED_TEST(InitializeAndDisposeMultiple) {
   for (int i = 0; i < 3; ++i) CHECK(v8::V8::Dispose());
 }
 
+// Tests that Smi::kZero is set up properly.
+UNINITIALIZED_TEST(SmiZero) { CHECK_EQ(i::Smi::kZero, i::Smi::kZero); }
 
 THREADED_TEST(Handles) {
   v8::HandleScope scope(CcTest::isolate());