SkPDF: allow PDF module to be disabled in DM and SampleApp

gyp/SampleApp.gyp

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
 {
   'includes': [
     'apptype_console.gypi',
   ],
   'targets': [
@@ skipping 235 matching lines @@
         [ 'skia_os == "chromeos"', {
           'sources!': [
             '../samplecode/SampleLighting.cpp',  #doesn't compile due to gpu dependencies
           ],
         }],
         [ 'skia_gpu == 1', {
           'dependencies': [
             'gputest.gyp:skgputest',
           ],
         }],
+        [ 'not skia_pdf', {
+          'dependencies!': [ 'pdf.gyp:pdf' ],
+          'dependencies': [ 'pdf.gyp:nopdf' ],
+        }],
       ],
     },
   ],
 }