[wasm] [asmjs] Route asm.js warnings to the dev console.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index a9a17b458bb45330d0a903598b181c51decb5c30..b3a5c49a103c8dc3661b8c0ba643603ce89c181a 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -399,6 +399,18 @@ void Utils::ReportOOMFailure(const char* location, bool is_heap_oom) {
   isolate->SignalFatalError();
 }
 
+void Utils::ReportAsmJsWarning(i::Handle<i::JSMessageObject> message) {
+  i::Isolate* isolate = i::Isolate::Current();
+  AsmJsWarningCallback asmjs_warning_callback =
+      isolate->asmjs_warning_behavior();
+  if (asmjs_warning_callback == nullptr) {
+    v8::internal::PrintF(
+        "%s\n", i::MessageHandler::GetLocalizedMessage(isolate, message).get());
+  } else {
+    asmjs_warning_callback(MessageToLocal(message));
+  }
+}
+
 static inline bool IsExecutionTerminatingCheck(i::Isolate* isolate) {
   if (isolate->has_scheduled_exception()) {
     return isolate->scheduled_exception() ==
@@ -8424,6 +8436,11 @@ void Isolate::SetOOMErrorHandler(OOMErrorCallback that) {
   isolate->set_oom_behavior(that);
 }
 
+void Isolate::SetAsmJsWarningHandler(AsmJsWarningCallback that) {
+  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
+  isolate->set_asmjs_warning_behavior(that);
+}
+
 void Isolate::SetAllowCodeGenerationFromStringsCallback(
     AllowCodeGenerationFromStringsCallback callback) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);