Remove iframe size check

Since we now only enable annotation of iframes that are explicitly opted
in by the containing page, we can avoid checking the size of the iframe
as well. That check was originally added to filter out ads and hidden
iframes.

This resolves an issue with Epub.js where an iframe initially has zero
width. This is because book content is laid out into a variable number
of fixed-width columns and the iframe's width is set to the total width
of all columns. Until the content is loaded, the number of columns and
hence the width, is zero.

src/annotator/util/frame-util.js

@@ -55,20 +55,14 @@ function shouldEnableAnnotation(iframe) {
   // Ignore the Hypothesis sidebar.
   const isNotClientFrame = !iframe.classList.contains('h-sidebar-iframe');
 
-  // Ignore hidden or very small iframes.
-  const frameRect = iframe.getBoundingClientRect();
-  const MIN_WIDTH = 150;
-  const MIN_HEIGHT = 150;
-  const hasSizableContainer =
-    frameRect.width > MIN_WIDTH && frameRect.height > MIN_HEIGHT;
-
-  // Ignore frames which have not opted into annotation support.
-  // Eventually we would like iframe annotation to be enabled by default,
-  // however we need to resolve a number of issues with iframe support before we
+  // Require iframes to opt into annotation support.
+  //
+  // Eventually we may want annotation to be enabled by default for iframes that
+  // pass certain tests. However we need to resolve a number of issues before we
   // can do that. See https://github.com/hypothesis/client/issues/530
   const enabled = iframe.hasAttribute('enable-annotation');
 
-  return isNotClientFrame && hasSizableContainer && enabled;
+  return isNotClientFrame && enabled;
 }
 
 function isDocumentReady(iframe, callback) {

src/annotator/util/test/frame-util-test.js

@@ -40,16 +40,6 @@ describe('annotator.util.frame-util', function () {
       assert.deepEqual(foundFrames, [frame1, frame2], 'appended frames should be found');
     });
 
-    it('should not return small frames', function () {
-      // add frames that are small in both demensions
-      _addFrameToContainer({width: 140});
-      _addFrameToContainer({height: 140});
-
-      const foundFrames = frameUtil.findFrames(container);
-
-      assert.lengthOf(foundFrames, 0, 'frames with small demensions should not be found');
-    });
-
     it('should not return frames that have not opted into annotation', () => {
       const frame = _addFrameToContainer();