Fix new -Wconstant-conversion versions after clang r259271

tools/battor_agent/battor_connection_impl_unittest.cc

 // Copyright 2015 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 "tools/battor_agent/battor_connection_impl.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/memory/weak_ptr.h"
 #include "base/test/test_simple_task_runner.h"
@@ skipping 180 matching lines @@
   ASSERT_EQ(BATTOR_MESSAGE_TYPE_CONTROL, GetReadType());
   ASSERT_EQ(0, std::memcmp(GetReadMessage()->data(), expected, 5));
 }
 
 TEST_F(BattOrConnectionImplTest, ReadMessageInvalidType) {
   OpenConnection();
   ASSERT_TRUE(GetOpenSuccess());
 
   const char data[] = {
       BATTOR_CONTROL_BYTE_START,
-      UINT8_MAX,
+      static_cast<char>(UINT8_MAX),
       BATTOR_CONTROL_BYTE_ESCAPE,
       BATTOR_CONTROL_MESSAGE_TYPE_RESET,
       0x04,
       0x04,
       0x04,
       0x04,
       BATTOR_CONTROL_BYTE_END,
   };
   SendBytesRaw(data, 7);
   ReadMessage(BATTOR_MESSAGE_TYPE_CONTROL);
@@ skipping 175 matching lines @@
       BATTOR_CONTROL_BYTE_END,
   };
   SendBytesRaw(data, 3);
   ReadMessage(BATTOR_MESSAGE_TYPE_PRINT);
 
   ASSERT_TRUE(IsReadComplete());
   ASSERT_FALSE(GetReadSuccess());
 }
 
 }  // namespace battor