Include implicit_cast.h at all users of it.

util/file/string_file.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/file/string_file.h"
 
 #include <string.h>
 
 #include <algorithm>
 #include <limits>
 
 #include "base/logging.h"
 #include "base/numerics/safe_math.h"
+#include "util/misc/implicit_cast.h"
 #include "util/numeric/safe_assignment.h"
 
 namespace crashpad {
 
 StringFile::StringFile() : string_(), offset_(0) {
 }
 
 StringFile::~StringFile() {
 }
 
@@ skipping 128 matching lines @@
                << " invalid for size_t";
     return -1;
   }
 
   offset_ = new_offset_sizet;
 
   return offset_.ValueOrDie();
 }
 
 }  // namespace crashpad