[Extensions] Initial implementation of checking toolbar icon visibility.

The toolbar icon is a visible indicator to the user that an extension is installed. Thus, a bad actor can attempt to hide the icon to disguise its presence. In addition, the icon allows the user an easy way to uninstall it.

Bug: 805600
Change-Id: I178901d03b8ce6b13b70932114bbf9747890ae9d
Reviewed-on: https://chromium-review.googlesource.com/1144253
Commit-Queue: David Bertoni <dbertoni@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577057}

extensions/common/image_util.cc

@@ -12,6 +12,7 @@
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "third_party/re2/src/re2/re2.h"
+#include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/utils/SkParse.h"
 #include "ui/gfx/color_utils.h"
@@ -158,5 +159,33 @@ bool ParseHslColorString(const std::string& color_string, SkColor* result) {
   return true;
 }
 
+bool IsIconSufficientlyVisible(const SkBitmap& bitmap) {
+  // TODO(crbug.com/805600): Currently, we only consider if there are enough
+  // visible pixels that it won't be difficult for the user to see. Future
+  // revisions will consider the background color of the display context.
+
+  // If the alpha value of any pixel is greater than kAlphaThreshold, the
+  // pixmap is not transparent. These values will likely be adjusted, based
+  // on stats and research into visibility thresholds.
+  constexpr unsigned int kAlphaThreshold = 10;
+  // The minimum "percent" of pixels that must be visible for the icon to be
+  // considered OK.
+  constexpr double kMinPercentVisiblePixels = 0.05;
+  const unsigned int total_pixels = bitmap.height() * bitmap.width();
+  unsigned int visible_pixels = 0;
+  for (int y = 0; y < bitmap.width(); ++y) {
+    for (int x = 0; x < bitmap.height(); ++x) {
+      if (SkColorGetA(bitmap.getColor(x, y)) >= kAlphaThreshold) {
+        ++visible_pixels;
+      }
+    }
+  }
+  // TODO(crbug.com/805600): Add UMA stats when we move to a more
+  // sophisticated analysis of the image and the background display
+  // color.
+  return static_cast<double>(visible_pixels) / total_pixels >=
+         kMinPercentVisiblePixels;
+}
+
 }  // namespace image_util
 }  // namespace extensions

extensions/common/image_util.h

@@ -7,6 +7,8 @@
 
 #include <string>
 
+class SkBitmap;
+
 typedef unsigned int SkColor;
 
 // This file contains various utility functions for extension images and colors.
@@ -30,6 +32,10 @@ bool ParseRgbColorString(const std::string& color_string, SkColor* result);
 // Parses hsl() or hsla() string to a SkColor. Returns true for success.
 bool ParseHslColorString(const std::string& color_string, SkColor* result);
 
+// Analyzes an icon image to determine if it will be visible in its display
+// context.
+bool IsIconSufficientlyVisible(const SkBitmap& bitmap);
+
 }  // namespace image_util
 }  // namespace extensions
 

extensions/common/image_util_unittest.cc

@@ -4,11 +4,31 @@
 
 #include <string>
 
+#include "base/files/file_path.h"
+#include "base/files/file_util.h"
+#include "base/path_service.h"
+#include "extensions/common/extension_paths.h"
 #include "extensions/common/image_util.h"
 #include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkColor.h"
+#include "ui/gfx/codec/png_codec.h"
 #include "ui/gfx/color_utils.h"
 
+namespace {
+
+bool LoadPngFromFile(const base::FilePath& path, SkBitmap* dst) {
+  std::string png_bytes;
+  if (!base::ReadFileToString(path, &png_bytes)) {
+    return false;
+  }
+  return gfx::PNGCodec::Decode(
+      reinterpret_cast<const unsigned char*>(png_bytes.data()),
+      png_bytes.length(), dst);
+}
+
+}  // namespace
+
 namespace extensions {
 
 void RunPassHexTest(const std::string& css_string, SkColor expected_result) {
@@ -176,4 +196,38 @@ TEST(ImageUtilTest, BasicColorKeyword) {
   EXPECT_FALSE(image_util::ParseCssColorString("my_red", &color));
 }
 
+TEST(ImageUtilTest, IsIconSufficientlyVisible) {
+  base::FilePath test_dir;
+  ASSERT_TRUE(base::PathService::Get(DIR_TEST_DATA, &test_dir));
+  base::FilePath icon_path;
+  {
+    // This icon has all transparent pixels, so it will fail.
+    icon_path = test_dir.AppendASCII("transparent_icon.png");
+    SkBitmap transparent_icon;
+    ASSERT_TRUE(LoadPngFromFile(icon_path, &transparent_icon));
+    EXPECT_FALSE(image_util::IsIconSufficientlyVisible(transparent_icon));
+  }
+  {
+    // Test with an icon that has one opaque pixel.
+    icon_path = test_dir.AppendASCII("one_pixel_opaque_icon.png");
+    SkBitmap visible_icon;
+    ASSERT_TRUE(LoadPngFromFile(icon_path, &visible_icon));
+    EXPECT_FALSE(image_util::IsIconSufficientlyVisible(visible_icon));
+  }
+  {
+    // Test with an icon that has one transparent pixel.
+    icon_path = test_dir.AppendASCII("one_pixel_transparent_icon.png");
+    SkBitmap visible_icon;
+    ASSERT_TRUE(LoadPngFromFile(icon_path, &visible_icon));
+    EXPECT_TRUE(image_util::IsIconSufficientlyVisible(visible_icon));
+  }
+  {
+    // Test with an icon that is completely opaque.
+    icon_path = test_dir.AppendASCII("opaque_icon.png");
+    SkBitmap visible_icon;
+    ASSERT_TRUE(LoadPngFromFile(icon_path, &visible_icon));
+    EXPECT_TRUE(image_util::IsIconSufficientlyVisible(visible_icon));
+  }
+}
+
 }  // namespace extensions