Pdfviewer: generate isAFoo() and getAsFoo() api for fields that can have multiple types.

experimental/PdfViewer/datatypes.py

 
 class PdfName:
   def __init__(self, name, abr=''):
     self.fName = name
     self.fAbr = abr
     
   def toCpp(self):
     return '\"' + self.fName + '\"'
 
 class PdfString:
@@ skipping 27 matching lines @@
 class PdfBoolean:
   def __init__(self, value):
     self.fValue = value
 
   def toCpp(self):
     return self.fValue
 
 class CppNull:
   def toCpp(self):
     return 'NULL'
+    
+class PdfDateNever:
+  def toCpp(self):
+    return 'SkPdfDate()'
+
+class FileSpecNone:
+  def toCpp(self):
+    return 'SkPdfFileSpec()'
+
+class PdfEmptyRect:
+  def toCpp(self):
+    return 'SkRect()'
+    
+class PdfEmptyStream:
+  def toCpp(self):
+    return 'SkPdfStream()'
+    
+class PdfArrayNone:
+  def toCpp(self):
+    return 'SkPdfArray()'
+    
+class PdfFunctionNone:
+  def toCpp(self):
+    return 'SkPdfFunction()'
+    
+