[turbofan] Properly type %_IsDate intrinsic.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/1208003002.

Cr-Commit-Position: refs/heads/master@{#29283}

src/compiler/typer.cc

@@ -1535,6 +1535,7 @@ Bounds Typer::Visitor::TypeJSCallRuntime(Node* node) {
     case Runtime::kInlineIsSmi:
     case Runtime::kInlineIsNonNegativeSmi:
     case Runtime::kInlineIsArray:
+    case Runtime::kInlineIsDate:
     case Runtime::kInlineIsTypedArray:
     case Runtime::kInlineIsMinusZero:
     case Runtime::kInlineIsFunction: