WebApp: Check pixel at the center of the generated icon.

We generate an icon placeholder using a letter with some solid
background color.

Let the test check if letter_color is actually presented in the icon.

This is a follow up test enhancement for the previous CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1888234

Bug: 1019102
Change-Id: I10e196926dff78032dcd8f00e93e24715d1be913
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1891816
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Reviewed-by: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711143}

chrome/browser/web_applications/components/web_app_icon_generator_unittest.cc

@@ -369,6 +369,7 @@ TEST_F(WebAppIconGeneratorTest, GenerateIconLetterFromUrl) {
 TEST_F(WebAppIconGeneratorTest, GenerateIcons) {
   std::set<int> sizes = SizesToGenerate();
   const SkColor bg_color = SK_ColorCYAN;
+  const SkColor letter_color = color_utils::GetColorWithMaxContrast(bg_color);
 
   // This is Unicode "Black Large Circle" U+2B24 character encoded as UTF8.
   // Guarantees that there is some letter_color area at the center of the
@@ -393,7 +394,15 @@ TEST_F(WebAppIconGeneratorTest, GenerateIcons) {
     // We don't check corner colors here: the icon is rounded by border_radius.
     EXPECT_EQ(bg_color, icon_info.data.getColor(border_radius * 2, center_y));
     EXPECT_EQ(bg_color, icon_info.data.getColor(center_x, border_radius * 2));
-    // TODO(loyso): Peek a pixel at the center of icon and check the color.
+
+    // Only for large icons with a sharp letter: Peek a pixel at the center of
+    // icon.
+    if (icon_info.width >= icon_size::k256) {
+      SkColor center_color = icon_info.data.getColor(center_x, center_y);
+      SCOPED_TRACE(letter_color);
+      SCOPED_TRACE(center_color);
+      EXPECT_TRUE(AreColorsEqual(letter_color, center_color, /*threshold=*/50));
+    }
 
     sizes.erase(icon_info.width);
   }