gyp_pdfium should use ninja by default.

build/gyp_pdfium

Index: build/gyp_pdfium
diff --git a/build/gyp_pdfium b/build/gyp_pdfium
index 7019795d095602ef0e18993437b90337edf93e70..fca2ca39b69977b01b105b53bf62271a880bd7f4 100755
--- a/build/gyp_pdfium
+++ b/build/gyp_pdfium
@@ -28,15 +28,20 @@ def run_gyp(args):
 def main():
   args = sys.argv[1:]
   args.append(os.path.join(script_dir, 'all.gyp'))
-  
+
   args.append('-I')
   args.append(os.path.join(pdfium_root, 'build', 'standalone.gypi'))
-  
+
   args.extend(['-D', 'gyp_output_dir=out'])
 
   # Set the GYP DEPTH variable to the root of the PDFium project.
   args.append('--depth=' + os.path.relpath(pdfium_root))
 
+  # GYP does not default to ninja, but PDFium should.
+  if not os.environ.get('GYP_GENERATORS', ''):
+    print 'GYP_GENERATORS is not set, defaulting to ninja'
+    os.environ['GYP_GENERATORS'] = 'ninja'
+
   print 'Updating projects from gyp files...'
   sys.stdout.flush()
 
@@ -44,4 +49,4 @@ def main():
 
 
 if __name__ == '__main__':
-  sys.exit(main())
+  sys.exit(main())