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>
diff --git a/src/semantic/sem_struct.cc b/src/semantic/sem_struct.cc
index 78c272a..d715863 100644
--- a/src/semantic/sem_struct.cc
+++ b/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() = 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,