FontAccess: Sort fonts in lexicographical order

This change ensures fonts are sorted before being cached. This change is
due to a concern about fingerprinting:
https://github.com/w3ctag/design-reviews/issues/399#issuecomment-530679815

This change ensures that fonts are sorted in lexicographical order.

Bug: 1043306
Change-Id: Ia3acf2a45cb473124df4e489683bdc7bac15dde4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2427040
Commit-Queue: Olivier Yiptong <oyiptong@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810519}

content/browser/font_access/font_access_manager_impl_unittest.cc

@@ -187,11 +187,19 @@ void ValidateFontEnumerationBasic(FontEnumerationStatus status,
   base::ReadOnlySharedMemoryMapping mapping = region.Map();
   table.ParseFromArray(mapping.memory(), mapping.size());
 
+  blink::FontEnumerationTable_FontMetadata previous_font;
   for (const auto& font : table.fonts()) {
     EXPECT_GT(font.postscript_name().size(), 0ULL)
         << "postscript_name size is not zero.";
     EXPECT_GT(font.full_name().size(), 0ULL) << "full_name size is not zero.";
     EXPECT_GT(font.family().size(), 0ULL) << "family size is not zero.";
+
+    if (previous_font.IsInitialized()) {
+      EXPECT_LT(previous_font.postscript_name(), font.postscript_name())
+          << "font list is sorted";
+    }
+
+    previous_font = font;
   }
 }
 

content/browser/font_access/font_enumeration_cache.cc

@@ -97,6 +97,12 @@ void FontEnumerationCache::BuildEnumerationCache(
     std::unique_ptr<blink::FontEnumerationTable> table) {
   DCHECK(!enumeration_cache_built_.IsSet());
 
+  std::sort(table->mutable_fonts()->begin(), table->mutable_fonts()->end(),
+            [](const blink::FontEnumerationTable_FontMetadata& a,
+               const blink::FontEnumerationTable_FontMetadata& b) {
+              return a.postscript_name() < b.postscript_name();
+            });
+
   enumeration_cache_memory_ =
       base::ReadOnlySharedMemoryRegion::Create(table->ByteSizeLong());
 

third_party/blink/web_tests/external/wpt/font-access/resources/window-tests-enumeration.js

@@ -31,3 +31,31 @@ font_access_test(async t => {
 
   assert_fonts_exist(availableFonts, getEnumerationTestSet());
 }, 'query(): standard fonts returned');
+
+font_access_test(async t => {
+  const iterator = navigator.fonts.query();
+
+  if (!isPlatformSupported()) {
+    await promise_rejects_dom(t, 'NotSupportedError', (async () => {
+      for await (const f of iterator) {
+      }
+    })());
+    return;
+  }
+
+  // The following tests that fonts are sorted. Postscript names are expected to
+  // be encoded in a subset of the ASCII character set.
+  // See: https://docs.microsoft.com/en-us/typography/opentype/spec/name
+  // Should the Postscript name contain characters that are multi-byte, this
+  // test may erroneously fail.
+  let previousFont = null;
+  for await (const font of iterator) {
+    if (previousFont) {
+      assert_true(
+          previousFont.postscriptName < font.postscriptName,
+          'fonts are sorted');
+    }
+
+    previousFont = font;
+  }
+}, 'query(): fonts are sorted');