Remove opaque alpha channel special case

third_party/WebKit/Source/platform/graphics/DeferredImageDecoderTest.cpp

Index: third_party/WebKit/Source/platform/graphics/DeferredImageDecoderTest.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/DeferredImageDecoderTest.cpp b/third_party/WebKit/Source/platform/graphics/DeferredImageDecoderTest.cpp
index 905b2d3830a6bff94ca44cb1de4d2cbbbd979b13..747a3cc5d8ae4a193e65f31967fafda34e879fbf 100644
--- a/third_party/WebKit/Source/platform/graphics/DeferredImageDecoderTest.cpp
+++ b/third_party/WebKit/Source/platform/graphics/DeferredImageDecoderTest.cpp
@@ -346,7 +346,9 @@ TEST_F(DeferredImageDecoderTest, frameOpacity) {
     Vector<char> storage(size);
     SkPixmap pixmap(pix_info, storage.data(), row_bytes);
 
-    // Before decoding, the frame is not known to be opaque.
+    // Before decoding, the frame's alpha is unknown and assumed to be
+    // transparent. This works well with partial decoding, which will be
+    // transparent until the full first frame is decoded.
     sk_sp<SkImage> frame = decoder->CreateFrameAtIndex(0);
     ASSERT_TRUE(frame);
     EXPECT_FALSE(frame->isOpaque());
@@ -354,10 +356,11 @@ TEST_F(DeferredImageDecoderTest, frameOpacity) {
     // Force a lazy decode by reading pixels.
     EXPECT_TRUE(frame->readPixels(pixmap, 0, 0));
 
-    // After decoding, the frame is known to be opaque.
     frame = decoder->CreateFrameAtIndex(0);
     ASSERT_TRUE(frame);
-    EXPECT_TRUE(frame->isOpaque());
+    // The GIF file used by this test is opaque.
+    // The PNG file used by this test (when test_gif is false) is transparent.

[scroggo_chromium, 2017/05/31 14:27:50]

The PNG file is actually an opaque white 1x1 image. We are just not currently
recognizing that it was PNG_COLOR_TYPE_RGB and has no tRNS chunk, so it must be
opaque.

But it seems like we should - just how in GIF we're considering a frame that
does not have a transparent pixel to be opaque, we should consider this PNG to
be opaque.

[cblume, 2017/05/31 18:09:04]

Ooooh THAT is what you were saying.
Okay, I'll update the comment. I think I'll also create a separate bug for
adding that detection.

+    EXPECT_EQ(test_gif, frame->isOpaque());
 
     // Re-generating the opaque-marked frame should not fail.
     EXPECT_TRUE(frame->readPixels(pixmap, 0, 0));