Remove one warning from PDFium compilation in Cros

core/fpdfapi/fpdf_font/fpdf_font_cid.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "core/fpdfapi/fpdf_font/font_int.h"
 
 #include "core/fpdfapi/fpdf_cmaps/cmap_int.h"
 #include "core/fpdfapi/fpdf_font/ttgsubtable.h"
@@ skipping 173 matching lines @@
 
 CIDSet CIDSetFromSizeT(size_t index) {
   if (index >= CIDSET_NUM_SETS) {
     NOTREACHED();
     return CIDSET_UNKNOWN;
   }
   return static_cast<CIDSet>(index);
 }
 
 CFX_ByteStringC CMap_GetString(const CFX_ByteStringC& word) {
-  return word.Mid(1, word.GetLength() - 2);
+  if (word.GetLength() <= 2)
+    return CFX_ByteStringC();
+  return CFX_ByteStringC(&word[1], word.GetLength() - 2);
 }
 
 int CompareDWORD(const void* data1, const void* data2) {
   return (*(uint32_t*)data1) - (*(uint32_t*)data2);
 }
 
 int CompareCID(const void* key, const void* element) {
   if ((*(uint32_t*)key) < (*(uint32_t*)element)) {
     return -1;
   }
@@ skipping 581 matching lines @@
   FPDFAPI_LoadCID2UnicodeMap(charset, m_pEmbeddedMap, m_EmbeddedCount);
 }
 
 CIDSet CharsetFromOrdering(const CFX_ByteStringC& ordering) {
   for (size_t charset = 1; charset < FX_ArraySize(g_CharsetNames); ++charset) {
     if (ordering == g_CharsetNames[charset])
       return CIDSetFromSizeT(charset);
   }
   return CIDSET_UNKNOWN;
 }