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

This is a reland of 5a0adcbe

Let's exclude Win platform for now. This is a useful finding which
requires investigation.

Original change's description:
> 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}

Bug: 1019102
Change-Id: I2d01c2a9f5eb94107a4dfc4fea041bdb18871fc3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1892651
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Reviewed-by: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711164}

chrome/browser/web_applications/components/web_app_icon_generator_unittest.cc

@@ -9,6 +9,7 @@
 #include "base/stl_util.h"
 #include "base/strings/string16.h"
 #include "base/test/task_environment.h"
+#include "build/build_config.h"
 #include "chrome/browser/web_applications/test/web_app_icon_test_utils.h"
 #include "chrome/common/web_application_info.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -393,7 +394,21 @@ 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.
+    //
+    // TODO(crbug.com/1019102): Investigate if Win7 x64 doesn't generate
+    // unicode characters in our GeneratedIconImageSource implementation.
+#if !defined(OS_WIN)
+    const SkColor letter_color = color_utils::GetColorWithMaxContrast(bg_color);
+    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));
+    }
+#endif  // !defined(OS_WIN)
 
     sizes.erase(icon_info.width);
   }