[wasm][asm.js] Ensure final validation phase runs.

src/asmjs/asm-wasm-builder.cc

Index: src/asmjs/asm-wasm-builder.cc
diff --git a/src/asmjs/asm-wasm-builder.cc b/src/asmjs/asm-wasm-builder.cc
index 1d6757950af8f79ae7571c92999dca3580563b29..787b8981e8c67947f563308d08551ba36ff6bc52 100644
--- a/src/asmjs/asm-wasm-builder.cc
+++ b/src/asmjs/asm-wasm-builder.cc
@@ -67,6 +67,7 @@ class AsmWasmBuilderImpl final : public AstVisitor<AsmWasmBuilderImpl> {
         script_(script),
         typer_(typer),
         typer_failed_(false),
+        typer_finished_(false),
         breakable_blocks_(zone),
         foreign_variables_(zone),
         init_function_(nullptr),
@@ -122,6 +123,10 @@ class AsmWasmBuilderImpl final : public AstVisitor<AsmWasmBuilderImpl> {
     if (HasStackOverflow()) {
       return false;
     }
+    if (!typer_finished_) {
+      typer_->FailWithMessage("Module missing export section.");
+      typer_failed_ = true;
+    }
     if (typer_failed_) {
       return false;
     }
@@ -322,10 +327,16 @@ class AsmWasmBuilderImpl final : public AstVisitor<AsmWasmBuilderImpl> {
 
   void VisitReturnStatement(ReturnStatement* stmt) {
     if (scope_ == kModuleScope) {
+      if (typer_finished_) {
+        typer_->FailWithMessage("Module has multiple returns.");
+        typer_failed_ = true;
+        return;
+      }
       if (!typer_->ValidateAfterFunctionsPhase()) {
         typer_failed_ = true;
         return;
       }
+      typer_finished_ = true;
       scope_ = kExportScope;
       RECURSE(Visit(stmt->expression()));
       scope_ = kModuleScope;
@@ -1947,6 +1958,7 @@ class AsmWasmBuilderImpl final : public AstVisitor<AsmWasmBuilderImpl> {
   Handle<Script> script_;
   AsmTyper* typer_;
   bool typer_failed_;
+  bool typer_finished_;
   ZoneVector<std::pair<BreakableStatement*, bool>> breakable_blocks_;
   ZoneVector<ForeignVariable> foreign_variables_;
   WasmFunctionBuilder* init_function_;