Fix some crashes in GN.

tools/gn/parser_unittest.cc

 // Copyright (c) 2013 The Chromium 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 <iostream>
 #include <sstream>
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/input_file.h"
 #include "tools/gn/parser.h"
@@ skipping 163 matching lines @@
       "   FUNCTION(print)\n"
       "    LIST\n"
       "     LITERAL(\"hai\")\n";
   DoParserPrintTest(input, expected);
 }
 
 TEST(Parser, UnaryOp) {
   DoExpressionPrintTest("!foo",
       "UNARY(!)\n"
       " IDENTIFIER(foo)\n");
+
+  // No contents for binary operator.
+  DoExpressionErrorTest("a = !", 1, 5);
 }
 
 TEST(Parser, List) {
   DoExpressionPrintTest("[]", "LIST\n");
   DoExpressionPrintTest("[1,asd,]",
       "LIST\n"
       " LITERAL(1)\n"
       " IDENTIFIER(asd)\n");
   DoExpressionPrintTest("[1, 2+3 - foo]",
       "LIST\n"
@@ skipping 14 matching lines @@
   DoExpressionErrorTest("[,]", 1, 2);
   DoExpressionErrorTest("[a,,]", 1, 4);
 }
 
 TEST(Parser, Assignment) {
   DoParserPrintTest("a=2",
                     "BLOCK\n"
                     " BINARY(=)\n"
                     "  IDENTIFIER(a)\n"
                     "  LITERAL(2)\n");
+
+  DoExpressionErrorTest("a = ", 1, 3);
 }
 
 TEST(Parser, Accessor) {
   // Accessor indexing.
   DoParserPrintTest("a=b[c+2]",
                     "BLOCK\n"
                     " BINARY(=)\n"
                     "  IDENTIFIER(a)\n"
                     "  ACCESSOR\n"
                     "   b\n"  // AccessorNode is a bit weird in that it holds
@@ skipping 469 matching lines @@
 // freestanding block.
 TEST(Parser, StandaloneBlock) {
   DoParserErrorTest(
       "if (true) {\n"
       "}\n"
       "{\n"
       "  assert(false)\n"
       "}\n",
       3, 1);
 }