[wasm] Support undefined indirect table entries, behind a flag.

test/mjsunit/wasm/wasm-module-builder.js

Index: test/mjsunit/wasm/wasm-module-builder.js
diff --git a/test/mjsunit/wasm/wasm-module-builder.js b/test/mjsunit/wasm/wasm-module-builder.js
index 98a5026379fba4fac57edfc439121f6fbc8b0976..5c5df798fbc9126c780a50a2a26eb9f37a82f4f6 100644
--- a/test/mjsunit/wasm/wasm-module-builder.js
+++ b/test/mjsunit/wasm/wasm-module-builder.js
@@ -109,6 +109,8 @@ class WasmModuleBuilder {
     this.table = [];
     this.segments = [];
     this.explicit = [];
+    this.pad = null;
+    return this;
   }
 
   addStart(start_index) {
@@ -120,6 +122,11 @@ class WasmModuleBuilder {
     return this;
   }
 
+  addPadFunctionTable(size) {
+    this.pad = size;
+    return this;
+  }
+
   addExplicitSection(bytes) {
     this.explicit.push(bytes);
     return this;
@@ -331,6 +338,19 @@ class WasmModuleBuilder {
       });
     }
 
+    // Add an indirect function table pad section.
+    if (wasm.pad !== null) {
+      if (debug)
+        print("emitting indirect function table pad @ " + binary.length);
+      binary.emit_section(kDeclFunctionTablePad, section => {
+        section.emit_varint(wasm.pad);
+      });
+    }
+
+    // End the module.
+    if (debug) print("emitting end @ " + binary.length);
+    binary.emit_section(kDeclEnd, section => {});
+
     return binary;
   }