Add GN split_list function

tools/gn/functions_unittest.cc

Index: tools/gn/functions_unittest.cc
diff --git a/tools/gn/functions_unittest.cc b/tools/gn/functions_unittest.cc
index 22670710704c6969255185ae5b3c34ca2b910a50..c6681bf5909b78362e2c0a80c77abfbe5ef956e6 100644
--- a/tools/gn/functions_unittest.cc
+++ b/tools/gn/functions_unittest.cc
@@ -90,3 +90,39 @@ TEST(Functions, FunctionsWithBlock) {
   result = defined_with_scope.parsed()->Execute(setup.scope(), &err);
   EXPECT_TRUE(err.has_error());
 }
+
+TEST(Functions, SplitList) {
+  TestWithScope setup;
+
+  TestParseInput input(
+      // Empty input with varying result items.
+      "out1 = split_list([], 1)\n"
+      "out2 = split_list([], 3)\n"
+      "print(\"empty = $out1 $out2\")\n"
+
+      // One item input.
+      "out3 = split_list([1], 1)\n"
+      "out4 = split_list([1], 2)\n"
+      "print(\"one = $out3 $out4\")\n"
+
+      // Multiple items.
+      "out5 = split_list([1, 2, 3, 4, 5, 6, 7, 8, 9], 2)\n"
+      "print(\"many = $out5\")\n"
+
+      // Rounding.
+      "out6 = split_list([1, 2, 3, 4, 5, 6], 4)\n"
+      "print(\"rounding = $out6\")\n"
+      );
+  ASSERT_FALSE(input.has_error());
+
+  Err err;
+  input.parsed()->Execute(setup.scope(), &err);
+  ASSERT_FALSE(err.has_error()) << err.message();
+
+  EXPECT_EQ(
+      "empty = [[]] [[], [], []]\n"
+      "one = [[1]] [[1], []]\n"
+      "many = [[1, 2, 3, 4, 5], [6, 7, 8, 9]]\n"
+      "rounding = [[1, 2], [3, 4], [5], [6]]\n",
+      setup.print_output());
+}