Remove opaque alpha channel special case

third_party/WebKit/Source/platform/image-decoders/bmp/BMPImageReader.h

Index: third_party/WebKit/Source/platform/image-decoders/bmp/BMPImageReader.h
diff --git a/third_party/WebKit/Source/platform/image-decoders/bmp/BMPImageReader.h b/third_party/WebKit/Source/platform/image-decoders/bmp/BMPImageReader.h
index c5bf44b401205a428dcf0f7e6aa4460a2c2221d1..72be7e1b2b2ce8e4119e04174653d9cc13e05a23 100644
--- a/third_party/WebKit/Source/platform/image-decoders/bmp/BMPImageReader.h
+++ b/third_party/WebKit/Source/platform/image-decoders/bmp/BMPImageReader.h
@@ -241,9 +241,10 @@ class PLATFORM_EXPORT BMPImageReader final {
                : value;
   }
 
+  inline bool IsAlphaSupported() const { return !bit_masks_[3]; }
+
   inline unsigned GetAlpha(uint32_t pixel) const {
-    // For images without alpha, return alpha of 0xff.
-    return bit_masks_[3] ? GetComponent(pixel, 3) : 0xff;
+    return GetComponent(pixel, 3);

[scroggo_chromium, 2017/05/08 14:56:36]

Previously, this was only called if (bit_masks_[3]), which, in the new code is
!IsAlphaSupported(). But now, this method is only called if
(IsAlphaSupported()). It seems like this got flipped?

[cblume, 2017/05/25 09:45:37]

Huh. Yeah.

IIUC, bit_masks_[3] is initialized at either
 * if IsWindowsV4Plus [1] with the value read, or
 * otherwise [2] with the value 0xff000000 or 0.

It seems like the value 0 means we don't yet know that there is alpha. This is
when it would begin checking for an alpha value other than 255.
So if no-alpha means bit_masks_[3] is 0, !bit_masks_[3] should return true if
there is no alpha.

That's the opposite of what I wanted. You're right.

[1]
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/platform/image...
[2]
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/platform/image...
[3]
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/platform/image...

   }
 
   // Sets the current pixel to the color given by |color_index|.  This also