[asmjs] Validator should reject modules with repeated functions.

src/typing-asm.cc

Index: src/typing-asm.cc
diff --git a/src/typing-asm.cc b/src/typing-asm.cc
index d98998520fae35bbc16c305979a6123df1be0cd7..fc6309141729c04842fddeb1c3ee2cdeaa177bf3 100644
--- a/src/typing-asm.cc
+++ b/src/typing-asm.cc
@@ -166,6 +166,10 @@ void AsmTyper::VisitFunctionDeclaration(FunctionDeclaration* decl) {
   // Set function type so global references to functions have some type
   // (so they can give a more useful error).
   Variable* var = decl->proxy()->var();
+  if (GetVariableInfo(var)) {
+    // Detect previously-seen functions.
+    FAIL(decl->fun(), "function repeated in module");
+  }
   SetType(var, Type::Function());
 }