Use fractions instead of percentages for metrics

Use fractions instead of percentages for the character and line metrics
in ImageTextLayer tests, for consistency with the ImageTextLayer API.

src/annotator/integrations/test/image-text-layer-test.js

 import { ImageTextLayer } from '../image-text-layer';
 
-// Sizes of characters and lines used in character bounding boxes generated by
-// these tests, expressed as percentages of the image size.
-const charWidth = 4;
-const charHeight = 8;
-const charSpacing = 5;
-const lineSpacing = 10;
+// Sizes and spacing between character bounding boxes in these tests, expressed
+// as fractions of the image size.
+const charWidth = 0.04;
+const charHeight = 0.08;
+const charSpacing = 0.05;
+const lineSpacing = 0.1;
 
 /**
  * Return a `[left, top, width, height]` tuple of the expected position of
  * a word in the text layer.
  */
 function expectedBoxOffsetAndSize(imageWidth, imageHeight, lineIndex, text) {
-  const xScale = imageWidth / 100;
-  const yScale = imageHeight / 100;
+  const width =
+    (text.length - 1) * charSpacing * imageWidth + charWidth * imageWidth;
+  const height = charHeight * imageHeight;
 
-  const width = (text.length - 1) * charSpacing * xScale + charWidth * xScale;
-  const height = charHeight * yScale;
-
-  return [0, lineSpacing * lineIndex * yScale, width, height];
+  return [0, lineSpacing * lineIndex * imageHeight, width, height].map(coord =>
+    Math.round(coord)
+  );
 }
 
 /**
@@ -33,10 +33,10 @@ function createCharBoxes(text) {
 
   for (let char of text) {
     charBoxes.push({
-      left: (charIndex * charSpacing) / 100,
-      right: (charIndex * charSpacing + charWidth) / 100,
-      top: (lineIndex * lineSpacing) / 100,
-      bottom: (lineIndex * lineSpacing + charHeight) / 100,
+      left: charIndex * charSpacing,
+      right: charIndex * charSpacing + charWidth,
+      top: lineIndex * lineSpacing,
+      bottom: lineIndex * lineSpacing + charHeight,
     });
 
     if (char === ' ') {