Add support for tiles in DefaultImageScalingFactory.

plone.app.tiles has its [own image scale factory](https://github.com/plone/plone.app.tiles/blob/3.2.2/plone/app/tiles/imagescaling.py#L110).
It [passes this around](https://github.com/plone/plone.app.tiles/blob/3.2.2/plone/app/tiles/imagescaling.py#L180) in a [deprecated way](https://github.com/plone/plone.scale/blob/3.1.2/plone/scale/storage.py#L207-L212).
Its scale factory does almost the same as the DefaultImageScalingFactory, although it is structured differently, as a function instead of a class.
Result is that the tiles scale factory is missing some features and fixes from the default, at least support for SVG and passing a quality parameter.

The only *intended* difference of the tile scale factory, is that it gets the original field value from the [tile data](https://github.com/plone/plone.app.tiles/blob/3.2.2/plone/app/tiles/imagescaling.py#L114),
instead of a [field on the context](https://github.com/plone/plone.namedfile/blob/5.5.1/plone/namedfile/scaling.py#L214).

The current commit makes the DefaultImageScalingFactory work for tiles.
Next step would be to update plone.app.tiles to use this.  This mostly involves removing code.

(Maybe something similar would be useful/needed for images in portlets, but I did not check. Do scales of images fields in portlets even work today?)

This will also make future support for focal points easier: there will be just one scaling factory to fix, instead of two.

news/104.feature

@@ -0,0 +1,2 @@
+Add support for tiles in DefaultImageScalingFactory.
+[maurits]

plone/namedfile/scaling.py

@@ -36,6 +36,11 @@
 import six
 
 
+try:
+    from plone.tiles.interfaces import IPersistentTile
+except ImportError:
+    IPersistentTile = None
+
 logger = logging.getLogger(__name__)
 _marker = object()
 
@@ -186,6 +191,32 @@ def traverse(self, name, furtherPath):
 class DefaultImageScalingFactory(object):
     def __init__(self, context):
         self.context = context
+        # fieldname will be set for real in the __call__ method.
+        self.fieldname = None
+        if IPersistentTile is not None and IPersistentTile.providedBy(context):
+            self.is_tile = True
+            # We get data from the tile:
+            self.data_context = context.data
+            # This is the actual content item (Page, News Item, etc):
+            self.content_context = context.context
+        else:
+            self.is_tile = False
+            self.data_context = context
+            self.content_context = context
+
+    def get_original_value(self):
+        if self.fieldname is None:
+            return
+        if self.is_tile:
+            return self.data_context.get(self.fieldname)
+        return getattr(self.content_context, self.fieldname, None)
+
+    def url(self):
+        # The url is useful when logging a problem.
+        base = self.content_context.absolute_url()
+        if not self.is_tile:
+            return base
+        return "{}/@@{}/{}".format(base, self.context.__name__, self.context.id)
 
     def get_quality(self):
         """Get plone.app.imaging's quality setting"""
@@ -211,7 +242,15 @@ def __call__(
 
         """Factory for image scales`.
         """
-        orig_value = getattr(self.context, fieldname, None)
+        if fieldname is None:
+            primary = IPrimaryFieldInfo(self.context, None)
+            if primary is None:
+                return
+            fieldname = primary.fieldname
+        # Safe self.fieldname for use in self.get_original_value.
+        self.fieldname = fieldname
+
+        orig_value = self.get_original_value()
         if orig_value is None:
             return
 
@@ -258,7 +297,7 @@ def __call__(
             except Exception:
                 logger.exception(
                     'Could not scale "{0!r}" of {1!r}'.format(
-                        orig_value, self.context.absolute_url(),
+                        orig_value, self.url(),
                     ),
                 )
                 return

setup.py

@@ -5,7 +5,7 @@
 import os
 
 
-version = '5.5.2.dev0'
+version = '5.6.0.dev0'
 
 description = 'File types and fields for images, files and blob files with ' \
               'filenames'