[Extensions] Reduce the percentage of visible pixels required.

This CL also adds a new utility function to render the icon to be
checked. A follow-up CL will add a unit test to reproduce the analysis
that led to lowering this number.

Bug: 805600
Change-Id: I7b93e1eececa4bb70659d8a89f782d0d9cbc5f44
Reviewed-on: https://chromium-review.googlesource.com/c/1431478Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: David Bertoni <dbertoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626215}

extensions/common/image_util.cc

@@ -233,7 +233,7 @@ bool IsRenderedIconSufficientlyVisible(const SkBitmap& icon,
   constexpr unsigned int kThreshold = 7;
   // The minimum "percent" of pixels that must be visible for the icon to be
   // considered OK.
-  constexpr double kMinPercentVisiblePixels = 0.05;
+  constexpr double kMinPercentVisiblePixels = 0.03;
   const int total_pixels = icon.height() * icon.width();
   // Pre-calculate the minimum number of visible pixels so we can exit early.
   // Since we expect most icons to be visible, this will perform better for
@@ -246,11 +246,8 @@ bool IsRenderedIconSufficientlyVisible(const SkBitmap& icon,
   // values against the threshold. Any pixel with a value greater than the
   // threshold is considered visible.
   SkBitmap bitmap;
-  bitmap.allocN32Pixels(icon.width(), icon.height());
-  bitmap.eraseColor(background_color);
-  SkCanvas offscreen(bitmap);
-  offscreen.drawImage(SkImage::MakeFromBitmap(icon), 0, 0);
-  offscreen.drawColor(background_color, SkBlendMode::kDifference);
+  RenderIconForVisibilityAnalysis(icon, background_color, &bitmap);
+
   int visible_pixels = 0;
   for (int x = 0; x < icon.width(); ++x) {
     for (int y = 0; y < icon.height(); ++y) {
@@ -266,6 +263,18 @@ bool IsRenderedIconSufficientlyVisible(const SkBitmap& icon,
   return false;
 }
 
+void RenderIconForVisibilityAnalysis(const SkBitmap& icon,
+                                     SkColor background_color,
+                                     SkBitmap* rendered_icon) {
+  DCHECK(rendered_icon);
+  DCHECK(rendered_icon->empty());
+  rendered_icon->allocN32Pixels(icon.width(), icon.height());
+  rendered_icon->eraseColor(background_color);
+  SkCanvas offscreen(*rendered_icon);
+  offscreen.drawImage(SkImage::MakeFromBitmap(icon), 0, 0);
+  offscreen.drawColor(background_color, SkBlendMode::kDifference);
+}
+
 bool IsRenderedIconAtPathSufficientlyVisible(const base::FilePath& path,
                                              SkColor background_color) {
   SkBitmap icon;

extensions/common/image_util.h

@@ -59,6 +59,12 @@ bool IsRenderedIconSufficientlyVisible(const SkBitmap& bitmap,
 bool IsRenderedIconAtPathSufficientlyVisible(const base::FilePath& path,
                                              SkColor background_color);
 
+// Renders the icon bitmap onto another bitmap, combining it with the specified
+// background color. The output bitmap must be empty.
+void RenderIconForVisibilityAnalysis(const SkBitmap& icon,
+                                     SkColor background_color,
+                                     SkBitmap* rendered_icon);
+
 // Load a PNG image from a file into the destination bitmap.
 bool LoadPngFromFile(const base::FilePath& path, SkBitmap* dst);