Make SVG painting independent of GraphicsContext's alpha state

Source/platform/graphics/GraphicsContext.h

Index: Source/platform/graphics/GraphicsContext.h
diff --git a/Source/platform/graphics/GraphicsContext.h b/Source/platform/graphics/GraphicsContext.h
index 75b8c56644bbdd2e967c99e3a65b8bf7e5e4d560..7a9660518003a603b50b89365f3f1e28b337792e 100644
--- a/Source/platform/graphics/GraphicsContext.h
+++ b/Source/platform/graphics/GraphicsContext.h
@@ -120,10 +120,10 @@ public:
     SkColor effectiveStrokeColor() const { return immutableState()->effectiveStrokeColor(); }
 
     Pattern* strokePattern() const { return immutableState()->strokePattern(); }
-    void setStrokePattern(PassRefPtr<Pattern>);
+    void setStrokePattern(PassRefPtr<Pattern>, float additionalAlpha = 1);
 
     Gradient* strokeGradient() const { return immutableState()->strokeGradient(); }
-    void setStrokeGradient(PassRefPtr<Gradient>);
+    void setStrokeGradient(PassRefPtr<Gradient>, float additionalAlpha = 1);
 
     void setLineCap(LineCap cap) { mutableState()->setLineCap(cap); }
     void setLineDash(const DashArray& dashes, float dashOffset) { mutableState()->setLineDash(dashes, dashOffset); }
@@ -137,10 +137,10 @@ public:
     void setFillColor(const Color& color) { mutableState()->setFillColor(color); }
     SkColor effectiveFillColor() const { return immutableState()->effectiveFillColor(); }
 
-    void setFillPattern(PassRefPtr<Pattern>);
+    void setFillPattern(PassRefPtr<Pattern>, float additionalAlpha = 1);
     Pattern* fillPattern() const { return immutableState()->fillPattern(); }
 
-    void setFillGradient(PassRefPtr<Gradient>);
+    void setFillGradient(PassRefPtr<Gradient>, float additionalAlpha = 1);
     Gradient* fillGradient() const { return immutableState()->fillGradient(); }
 
     SkDrawLooper* drawLooper() const { return immutableState()->drawLooper(); }
@@ -396,6 +396,13 @@ public:
     void setInDrawingRecorder(bool);
 #endif
 
+    // Multiply a color's alpha channel by an additional alpha factor. This is
+    // similar to Color::combineWithAlpha but uses Skia's rounding approach.
+    static SkColor combineWithAlpha(SkColor color, float alpha)
+    {
+        return GraphicsContextState::combineWithAlpha(color, alpha);
+    }
+
 private:
     const GraphicsContextState* immutableState() const { return m_paintState; }