[heap] Report proper OOM failure if semi-space copy fails.

src/heap/scavenger.cc

 // Copyright 2015 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/heap/scavenger.h"
 
 #include "src/contexts.h"
 #include "src/heap/heap.h"
 #include "src/heap/objects-visiting-inl.h"
 #include "src/heap/scavenger-inl.h"
@@ skipping 218 matching lines @@
     }
 
     if (PromoteObject<object_contents, alignment>(map, slot, object,
                                                   object_size)) {
       return;
     }
 
     // If promotion failed, we try to copy the object to the other semi-space
     if (SemiSpaceCopyObject<alignment>(map, slot, object, object_size)) return;
 
-    UNREACHABLE();
+    FatalProcessOutOfMemory("Scavenger: semi-space copy\n");
   }
 
 
   static inline void EvacuateJSFunction(Map* map, HeapObject** slot,
                                         HeapObject* object) {
     ObjectEvacuationStrategy<POINTER_OBJECT>::template VisitSpecialized<
         JSFunction::kSize>(map, slot, object);
 
     MapWord map_word = object->map_word();
     DCHECK(map_word.IsForwardingAddress());
@@ skipping 237 matching lines @@
 
 void ScavengeVisitor::ScavengePointer(Object** p) {
   Object* object = *p;
   if (!heap_->InNewSpace(object)) return;
   Scavenger::ScavengeObject(reinterpret_cast<HeapObject**>(p),
                             reinterpret_cast<HeapObject*>(object));
 }
 
 }  // namespace internal
 }  // namespace v8