[asm.js] Remove dead nullptr check of signatures.

R=clemensh@chromium.org

Change-Id: I616a972283cc85ccaf63c46d0cc11ccbb7563a46
Reviewed-on: https://chromium-review.googlesource.com/504527Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45289}

src/asmjs/asm-parser.cc

@@ -156,7 +156,7 @@ FunctionSig* AsmJsParser::ConvertSignature(
     } else if (param->IsA(AsmType::Int())) {
       sig_builder.AddParam(kWasmI32);
     } else {
-      return nullptr;
+      UNREACHABLE();
     }
   }
   if (!return_type->IsA(AsmType::Void())) {
@@ -167,7 +167,7 @@ FunctionSig* AsmJsParser::ConvertSignature(
     } else if (return_type->IsA(AsmType::Signed())) {
       sig_builder.AddReturn(kWasmI32);
     } else {
-      return 0;
+      UNREACHABLE();
     }
   }
   return sig_builder.Build();
@@ -767,9 +767,6 @@ void AsmJsParser::ValidateFunction() {
   // TODO(bradnelson): WasmModuleBuilder can't take this in the right order.
   //                   We should fix that so we can use it instead.
   FunctionSig* sig = ConvertSignature(return_type_, params);
-  if (sig == nullptr) {
-    FAIL("Invalid function signature in declaration");
-  }
   current_function_builder_->SetSignature(sig);
   for (auto local : locals) {
     current_function_builder_->AddLocal(local);
@@ -2140,9 +2137,6 @@ AsmType* AsmJsParser::ValidateCall() {
     function_type->AsFunctionType()->AddArgument(t);
   }
   FunctionSig* sig = ConvertSignature(return_type, param_types);
-  if (sig == nullptr) {
-    FAILn("Invalid function signature");
-  }
   uint32_t signature_index = module_builder_->AddSignature(sig);
 
   // Emit actual function invocation depending on the kind. At this point we