chore: Raise screenshot threshold for native text (#7265)

The screenshots with native text rendering don't always trigger our
threshold even when they should. That's because the native text tends to
be much smaller. Therefore the matching threshold should be higher to
make these smaller regions of text more sensitive to change.

This raises the threshold from 95% (still used for DOM-based) to 97% for
native text. I believe this could have caught some of the changes that I
only caught later with manual review of screenshots.

Original author: @joeyparrish Thanks!

build/updateScreenshots.py

@@ -70,7 +70,8 @@ def main(args):
           # No original?  Then everything has changed!
           similarity = 0
 
-        if similarity >= 0.95:
+        threshold = 0.95 if '-ui-' in fullPath else 0.97
+        if similarity >= threshold:
           # Similar enough to pass tests, so don't update the image.  This will
           # keep the git history from getting bigger for no reason.
           continue

test/test/util/layout_tests.js

@@ -11,7 +11,8 @@
 
 
 // A minimum similarity score for screenshots, between 0 and 1.
-const minSimilarity = 0.95;
+const MIN_SIMILARITY_UI = 0.95;
+const MIN_SIMILARITY_NATIVE = 0.97;
 
 const originalCast = window.chrome && window.chrome.cast;
 
@@ -87,7 +88,7 @@ shaka.test.LayoutTests = class {
    * @param {number} minSimilarity A minimum similarity score between 0 and 1.
    * @return {!Promise}
    */
-  static async checkScreenshot(element, name, minSimilarity=1) {
+  static async checkScreenshot(element, name, minSimilarity) {
     // Make sure the DOM is up-to-date and layout has settled before continuing.
     // Without this delay, or with a shorter delay, we sometimes get missing
     // elements in our UITextDisplayer tests on some platforms.
@@ -167,6 +168,9 @@ shaka.test.TextLayoutTests = class extends shaka.test.LayoutTests {
 
     /** @type {shaka.extern.TextDisplayer} */
     this.textDisplayer = null;
+
+    /** @type {number} */
+    this.minSimilarity = MIN_SIMILARITY_NATIVE;
   }
 
   /** @override */
@@ -229,7 +233,7 @@ shaka.test.TextLayoutTests = class extends shaka.test.LayoutTests {
     return shaka.test.LayoutTests.checkScreenshot(
         /* element= */ this.videoContainer,
         this.prefix + '-' + baseName,
-        minSimilarity);
+        this.minSimilarity);
   }
 };
 
@@ -243,6 +247,9 @@ shaka.test.DomTextLayoutTests = class extends shaka.test.TextLayoutTests {
 
     /** @type {shaka.test.FakeVideo} */
     this.mockVideo = null;
+
+    /** @type {number} */
+    this.minSimilarity = MIN_SIMILARITY_UI;
   }
 
   /** @override */