Fix new -Wnull-conversion violations detected by a newer clang.

printing/pdf_metafile_skia.cc

 // Copyright (c) 2012 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 "printing/pdf_metafile_skia.h"
 
 #include "base/eintr_wrapper.h"
 #include "base/file_descriptor_posix.h"
 #include "base/file_util.h"
 #include "base/hash_tables.h"
@@ skipping 55 matching lines @@
       new skia::VectorPlatformDeviceSkia(pdf_page_size, pdf_content_size,
                                          transform);
   data_->current_page_ = pdf_device;
   return pdf_device.get();
 }
 
 bool PdfMetafileSkia::StartPage(const gfx::Size& page_size,
                                 const gfx::Rect& content_area,
                                 const float& scale_factor) {
   NOTREACHED();
-  return NULL;
+  return false;
 }
 
 bool PdfMetafileSkia::FinishPage() {
   DCHECK(data_->current_page_.get());
 
   data_->pdf_doc_.appendPage(data_->current_page_.get());
   page_outstanding_ = false;
   return true;
 }
 
@@ skipping 154 matching lines @@
   SkAutoDataUnref data(pdf_stream.copyToData());
   if (data.size() == 0)
     return NULL;
 
   PdfMetafileSkia* metafile = new PdfMetafileSkia;
   metafile->InitFromData(data.bytes(), data.size());
   return metafile;
 }
 
 }  // namespace printing