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

src/api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 381 matching lines @@
                      is_heap_oom
                          ? "Allocation failed - JavaScript heap out of memory"
                          : "Allocation failed - process out of memory");
     }
   } else {
     oom_callback(location, 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() ==
         isolate->heap()->termination_exception();
   }
   return false;
 }
 
 
 void V8::SetNativesDataBlob(StartupData* natives_blob) {
@@ skipping 8005 matching lines @@
 void Isolate::SetFatalErrorHandler(FatalErrorCallback that) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
   isolate->set_exception_behavior(that);
 }
 
 void Isolate::SetOOMErrorHandler(OOMErrorCallback that) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
   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);
   isolate->set_allow_code_gen_callback(callback);
 }
 
 
 bool Isolate::IsDead() {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
   return isolate->IsDead();
@@ skipping 1417 matching lines @@
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 }  // namespace internal
 }  // namespace v8