Include implicit_cast.h at all users of it.

util/posix/symbolic_constants_posix.cc

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 #include "util/posix/symbolic_constants_posix.h"
 
 #include <sys/signal.h>
 
 #include "base/basictypes.h"
 #include "base/strings/stringprintf.h"
+#include "util/misc/implicit_cast.h"
 #include "util/stdlib/string_number_conversion.h"
 
 namespace {
 
 const char* kSignalNames[] = {
     nullptr,
 
 #if defined(OS_MACOSX)
     // sed -Ene 's/^#define[[:space:]]SIG([[:alnum:]]+)[[:space:]]+[[:digit:]]{1,2}([[:space:]]|$).*/    "\1",/p'
     //     /usr/include/sys/signal.h
@@ skipping 126 matching lines @@
   }
 
   if (options & kAllowNumber) {
     return StringToNumber(string, signal);
   }
 
   return false;
 }
 
 }  // namespace crashpad