[wasm][asm.js] Add flag to optionally suppress asm.js messages.

Asm.js warnings / info is non-canonical.
It may be useful to suppress it in golden file tests
(for instance LayoutTests).

BUG=v8:4203
R=mtrofin@chromium.org

Review-Url: https://codereview.chromium.org/2625833003
Cr-Commit-Position: refs/heads/master@{#42204}

src/asmjs/asm-js.cc

@@ -170,9 +170,11 @@ MaybeHandle<FixedArray> AsmJs::CompileAsmViaWasm(CompilationInfo* info) {
   auto asm_wasm_result = builder.Run(&foreign_globals);
   if (!asm_wasm_result.success) {
     DCHECK(!info->isolate()->has_pending_exception());
+    if (!FLAG_suppress_asm_messages) {
       MessageHandler::ReportMessage(info->isolate(),
                                     builder.typer()->message_location(),
                                     builder.typer()->error_message());
+    }
     return MaybeHandle<FixedArray>();
   }
   double asm_wasm_time = asm_wasm_timer.Elapsed().InMillisecondsF();
@@ -226,7 +228,9 @@ MaybeHandle<FixedArray> AsmJs::CompileAsmViaWasm(CompilationInfo* info) {
       info->isolate(), MessageTemplate::kAsmJsCompiled, &location, stext,
       Handle<JSArray>::null());
   message->set_error_level(v8::Isolate::kMessageInfo);
+  if (!FLAG_suppress_asm_messages) {
     MessageHandler::ReportMessage(info->isolate(), &location, message);
+  }
 
   return result;
 }

src/flag-definitions.h

@@ -520,6 +520,8 @@ DEFINE_BOOL(wasm_loop_assignment_analysis, true,
 
 DEFINE_BOOL(validate_asm, false, "validate asm.js modules before compiling")
 DEFINE_IMPLICATION(ignition_staging, validate_asm)
+DEFINE_BOOL(suppress_asm_messages, false,
+            "don't emit asm.js related messages (for golden file testing)")
 DEFINE_BOOL(trace_asm_time, false, "log asm.js timing info to the console")
 
 DEFINE_BOOL(dump_wasm_module, false, "dump WASM module bytes")