semantic::Struct: Add FindMember

Change-Id: Ie7b76ad8b7dbac1303ed73ba6962e584fed76238
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/46628
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>

src/semantic/sem_struct.cc

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#include "src/ast/struct_member.h"
 #include "src/semantic/struct.h"
 
 TINT_INSTANTIATE_TYPEINFO(tint::semantic::Struct);
@@ -37,6 +38,15 @@ Struct::Struct(type::Struct* type,
 
 Struct::~Struct() = default;
 
+const StructMember* Struct::FindMember(Symbol name) const {
+  for (auto* member : members_) {
+    if (member->Declaration()->symbol() == name) {
+      return member;
+    }
+  }
+  return nullptr;
+}
+
 StructMember::StructMember(ast::StructMember* declaration,
                            uint32_t offset,
                            uint32_t align,

src/semantic/struct.h

@@ -79,6 +79,10 @@ class Struct : public Castable<Struct, Node> {
   /// @returns the members of the structure
   const StructMemberList& Members() const { return members_; }
 
+  /// @param name the member name to look for
+  /// @returns the member with the given name, or nullptr if it was not found.
+  const StructMember* FindMember(Symbol name) const;
+
   /// @returns the byte alignment of the structure
   /// @note this may differ from the alignment of a structure member of this
   /// structure type, if the member is annotated with the `[[align(n)]]`