Add "alpha" option to PaintWorklet

third_party/WebKit/Source/modules/csspaint/PaintRenderingContext2D.h

Index: third_party/WebKit/Source/modules/csspaint/PaintRenderingContext2D.h
diff --git a/third_party/WebKit/Source/modules/csspaint/PaintRenderingContext2D.h b/third_party/WebKit/Source/modules/csspaint/PaintRenderingContext2D.h
index 03b3fa65a15a3af1ace2a25a74309149e2ab2bb5..9ce602fc19701322f307c93d6417b0422508df0d 100644
--- a/third_party/WebKit/Source/modules/csspaint/PaintRenderingContext2D.h
+++ b/third_party/WebKit/Source/modules/csspaint/PaintRenderingContext2D.h
@@ -23,9 +23,9 @@ class MODULES_EXPORT PaintRenderingContext2D : public BaseRenderingContext2D, pu
     USING_GARBAGE_COLLECTED_MIXIN(PaintRenderingContext2D);
     WTF_MAKE_NONCOPYABLE(PaintRenderingContext2D);
 public:
-    static PaintRenderingContext2D* create(std::unique_ptr<ImageBuffer> imageBuffer)
+    static PaintRenderingContext2D* create(std::unique_ptr<ImageBuffer> imageBuffer, bool hasAlpha)
     {
-        return new PaintRenderingContext2D(std::move(imageBuffer));
+        return new PaintRenderingContext2D(std::move(imageBuffer), hasAlpha);
     }
 
     // BaseRenderingContext2D
@@ -62,15 +62,16 @@ public:
 
     void validateStateStack() final;
 
-    bool hasAlpha() const final { return true; }
+    bool hasAlpha() const final { return m_hasAlpha; }

[ikilpatrick, 2016/06/23 16:53:42]

This method can probably be now implemented as a non-virtual on
BaseRenderingContext2D instead?

[Gleb Lanbin, 2016/06/23 22:26:03]

I tried to pass hasAlpha directly to BaseRenderingContext2D but it didn't work.
For example CanvasRenderingContext2D doesn't call the super class constructor by
intention and it's not allowed to initialize   base class members from
initialization list directly.

 
     // PaintRenderingContext2D cannot lose it's context.
     bool isContextLost() const final { return false; }
 
 private:
-    explicit PaintRenderingContext2D(std::unique_ptr<ImageBuffer>);
+    PaintRenderingContext2D(std::unique_ptr<ImageBuffer>, bool hasAlpha);
 
     std::unique_ptr<ImageBuffer> m_imageBuffer;
+    bool m_hasAlpha;
 };
 
 } // namespace blink