[wasm] Add tests for re-importing into different instances

Since the code around that is quite fragile, and I plan to refactor it,
just add some tests to ensure that everything is and keeps working as
intended.

R=mstarzinger@chromium.org

Bug: v8:7758
Change-Id: Ib3814b93b465286d70b5669ed0161eecb9fc925a
Reviewed-on: https://chromium-review.googlesource.com/1059616Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53187}

test/mjsunit/wasm/import-function.js

@@ -294,8 +294,69 @@ function testImportName(name) {
   assertEquals(42, main());
 }
 
-testImportName("bla");
-testImportName("0");
-testImportName("  a @#$2 324 ");
-// TODO(bradnelson): This should succeed.
-// testImportName("");
+testImportName('bla');
+testImportName('0');
+testImportName('  a @#$2 324 ');
+testImportName('');
+
+(function testExportedImportsOnDifferentInstances() {
+  print(arguments.callee.name);
+  const exp = (function() {
+    const builder = new WasmModuleBuilder();
+    builder.addFunction('f11', kSig_i_v)
+        .addBody([kExprI32Const, 11])
+        .exportFunc();
+    builder.addFunction('f17', kSig_i_v)
+        .addBody([kExprI32Const, 17])
+        .exportFunc();
+    return builder.instantiate().exports;
+  })();
+
+  const builder = new WasmModuleBuilder();
+  const imp_index = builder.addImport('q', 'imp', kSig_i_v);
+  builder.addExport('exp', imp_index);
+
+  const module = builder.toModule();
+  const instance0 = new WebAssembly.Instance(module, {q: {imp: exp.f11}});
+  const instance1 = new WebAssembly.Instance(module, {q: {imp: exp.f17}});
+  const instance2 = new WebAssembly.Instance(module, {q: {imp: _ => 21}});
+  const instance3 = new WebAssembly.Instance(module, {q: {imp: _ => 27}});
+
+  assertEquals(11, instance0.exports.exp());
+  assertEquals(17, instance1.exports.exp());
+  assertEquals(21, instance2.exports.exp());
+  assertEquals(27, instance3.exports.exp());
+})();
+
+(function testImportedStartFunctionOnDifferentInstances() {
+  print(arguments.callee.name);
+  var global = 0;
+  const set_global = n => global = n;
+  const exp = (function() {
+    const builder = new WasmModuleBuilder();
+    const imp_index = builder.addImport('q', 'imp', kSig_v_i);
+    builder.addFunction('f11', kSig_v_v)
+        .addBody([kExprI32Const, 11, kExprCallFunction, imp_index])
+        .exportFunc();
+    builder.addFunction('f17', kSig_v_v)
+        .addBody([kExprI32Const, 17, kExprCallFunction, imp_index])
+        .exportFunc();
+    return builder.instantiate({q: {imp: set_global}}).exports;
+  })();
+
+  const builder = new WasmModuleBuilder();
+  const imp_index = builder.addImport('q', 'imp', kSig_v_v);
+  builder.addStart(imp_index);
+
+  const module = builder.toModule();
+
+  assertEquals(0, global);
+  new WebAssembly.Instance(module, {q: {imp: exp.f11}});
+  assertEquals(11, global);
+  new WebAssembly.Instance(module, {q: {imp: exp.f17}});
+  assertEquals(17, global);
+  new WebAssembly.Instance(module, {q: {imp: _ => set_global(21)}});
+  assertEquals(21, global);
+  new WebAssembly.Instance(module, {q: {imp: _ => set_global(27)}});
+  assertEquals(27, global);
+})();