[ubsan] Fix HeapObjectMatcher to avoid invalid casts.

src/compiler/js-intrinsic-lowering.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/compiler/js-intrinsic-lowering.h"
 
 #include <stack>
 
 #include "src/compiler/access-builder.h"
 #include "src/compiler/js-graph.h"
@@ skipping 161 matching lines @@
   Node* value = NodeProperties::GetValueInput(node, 0);
   Node* effect = NodeProperties::GetEffectInput(node);
   Node* control = NodeProperties::GetControlInput(node);
   return Change(node, simplified()->LoadField(AccessBuilder::ForMap()), value,
                 effect, control);
 }
 
 
 Reduction JSIntrinsicLowering::ReduceIncrementStatsCounter(Node* node) {
   if (!FLAG_native_code_counters) return ChangeToUndefined(node);
-  HeapObjectMatcher<String> m(NodeProperties::GetValueInput(node, 0));
+  HeapObjectMatcher m(NodeProperties::GetValueInput(node, 0));
   if (!m.HasValue() || !m.Value().handle()->IsString()) {
     return ChangeToUndefined(node);
   }
-  SmartArrayPointer<char> name = m.Value().handle()->ToCString();
+  SmartArrayPointer<char> name =
+      Handle<String>::cast(m.Value().handle())->ToCString();
   StatsCounter counter(jsgraph()->isolate(), name.get());
   if (!counter.Enabled()) return ChangeToUndefined(node);
 
   Node* effect = NodeProperties::GetEffectInput(node);
   Node* control = NodeProperties::GetControlInput(node);
   FieldAccess access = AccessBuilder::ForStatsCounter();
   Node* cnt = jsgraph()->ExternalConstant(ExternalReference(&counter));
   Node* load =
       graph()->NewNode(simplified()->LoadField(access), cnt, effect, control);
   Node* inc =
@@ skipping 344 matching lines @@
 }
 
 
 MachineOperatorBuilder* JSIntrinsicLowering::machine() const {
   return jsgraph()->machine();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8