Add result_type into ast::Expression

This CL adds a result_type into the expression to hold the computed
result type for the expression.

Bug: tint:5
Change-Id: I5f2ee35e520f918828cf8cf7bc6fdf6a1b5ebd5f
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/18824
Reviewed-by: David Neto <dneto@google.com>

src/ast/expression.h

@@ -16,6 +16,7 @@
 #define SRC_AST_EXPRESSION_H_
 
 #include "src/ast/node.h"
+#include "src/ast/type/type.h"
 
 namespace tint {
 namespace ast {
@@ -37,6 +38,12 @@ class Expression : public Node {
  public:
   ~Expression() override;
 
+  /// Sets the resulting type of this expression
+  /// @param type the result type to set
+  void set_result_type(type::Type* type) { result_type_ = type; }
+  /// @returns the resulting type from this expression
+  type::Type* result_type() const { return result_type_; }
+
   /// @returns true if this is an array accessor expression
   virtual bool IsArrayAccessor() const { return false; }
   /// @returns true if this is an as expression
@@ -94,6 +101,8 @@ class Expression : public Node {
 
  private:
   Expression(const Expression&) = delete;
+
+  type::Type* result_type_ = nullptr;
 };
 
 }  // namespace ast