Add a call ast statement.

This CL adds CallStatement to the AST to allow wrapping a CallExpression
into a statement.

Bug: tint:45
Change-Id: I5a9525514344fcc2cf9900eb2cd78c1fb94ca2ef
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/25320
Reviewed-by: David Neto <dneto@google.com>

src/ast/call_statement.h

diff --git a/src/ast/call_statement.h b/src/ast/call_statement.h
new file mode 100644
index 0000000..374136b
--- /dev/null
+++ b/src/ast/call_statement.h
@@ -0,0 +1,67 @@
+// Copyright 2020 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_AST_CALL_STATEMENT_H_
+#define SRC_AST_CALL_STATEMENT_H_
+
+#include <memory>
+#include <utility>
+
+#include "src/ast/call_expression.h"
+#include "src/ast/statement.h"
+
+namespace tint {
+namespace ast {
+
+/// A call expression
+class CallStatement : public Statement {
+ public:
+  /// Constructor
+  CallStatement();
+  /// Constructor
+  /// @param call the function
+  explicit CallStatement(std::unique_ptr<CallExpression> call);
+  /// Move constructor
+  CallStatement(CallStatement&&);
+  ~CallStatement() override;
+
+  /// Sets the call expression
+  /// @param call the call
+  void set_expr(std::unique_ptr<CallExpression> call) {
+    call_ = std::move(call);
+  }
+  /// @returns the call expression
+  CallExpression* expr() const { return call_.get(); }
+
+  /// @returns true if this is a call statement
+  bool IsCall() const override;
+
+  /// @returns true if the node is valid
+  bool IsValid() const override;
+
+  /// Writes a representation of the node to the output stream
+  /// @param out the stream to write to
+  /// @param indent number of spaces to indent the node when writing
+  void to_str(std::ostream& out, size_t indent) const override;
+
+ private:
+  CallStatement(const CallStatement&) = delete;
+
+  std::unique_ptr<CallExpression> call_;
+};
+
+}  // namespace ast
+}  // namespace tint
+
+#endif  // SRC_AST_CALL_STATEMENT_H_