Fix crash in DarkModeImageClassifier::GetSamples().

For classifying images, DarkModeImageClassifier creates bitmap from
PaintImage. For empty paint images, this crashes. This patch prevents
classifying such empty paint images.

Bug: 1119761
Change-Id: I3961da716236b929cc5a6925ff5927d5e8f8ac60
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2368935
Commit-Queue: Prashant Nevase <prashant.n@samsung.com>
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801267}

third_party/blink/renderer/platform/graphics/dark_mode_image_classifier.cc

@@ -110,6 +110,10 @@ DarkModeClassification DarkModeImageClassifier::Classify(
     const PaintImage& paint_image,
     const SkRect& src,
     const SkRect& dst) {
+  // Empty paint image cannot be classified.
+  if (!paint_image)
+    return DarkModeClassification::kDoNotApplyFilter;
+
   DarkModeImageClassificationCache* cache =
       DarkModeImageClassificationCache::GetInstance();
   PaintImage::Id image_id = paint_image.stable_id();
@@ -131,6 +135,8 @@ DarkModeClassification DarkModeImageClassifier::Classify(
 bool DarkModeImageClassifier::GetBitmap(const PaintImage& paint_image,
                                         const SkRect& src,
                                         SkBitmap* bitmap) {
+  DCHECK(paint_image);
+
   if (!src.width() || !src.height())
     return false;
 

third_party/blink/renderer/platform/graphics/dark_mode_image_classifier_test.cc

@@ -150,6 +150,14 @@ TEST_F(DarkModeImageClassifierTest, FeaturesAndClassification) {
   EXPECT_NEAR(0.0f, features.background_ratio, kEpsilon);
 }
 
+TEST_F(DarkModeImageClassifierTest, InvalidImage) {
+  PaintImage paint_image;
+  SkRect src = SkRect::MakeWH(50, 50);
+  SkRect dst = SkRect::MakeWH(50, 50);
+  EXPECT_EQ(image_classifier()->Classify(paint_image, src, dst),
+            DarkModeClassification::kDoNotApplyFilter);
+}
+
 TEST_F(DarkModeImageClassifierTest, Caching) {
   PaintImage::Id image_id = PaintImage::GetNextId();
   SkRect src1 = SkRect::MakeXYWH(0, 0, 50, 50);