[turbofan] Check that inputs to Node::New are not NULL.

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1492433003

Cr-Commit-Position: refs/heads/master@{#32472}

src/compiler/node.cc

@@ -56,6 +56,16 @@ Node* Node::New(Zone* zone, NodeId id, const Operator* op, int input_count,
   Node* node;
   bool is_inline;
 
+#if DEBUG
+  // Verify that none of the inputs are {nullptr}.
+  for (int i = 0; i < input_count; i++) {
+    if (inputs[i] == nullptr) {
+      V8_Fatal(__FILE__, __LINE__, "Node::New() Error: #%d:%s[%d] is NULL",
+            static_cast<int>(id), op->mnemonic(), i);
+    }
+  }
+#endif
+
   if (input_count > kMaxInlineCapacity) {
     // Allocate out-of-line inputs.
     int capacity =