Bug 1489632 - mark Skia bitmap layer as immutable before popping it. r=rhunt

gfx/skia/skia/src/core/SkBitmapDevice.h

@@ -119,6 +119,7 @@ protected:
     sk_sp<SkSpecialImage> makeSpecial(const SkBitmap&) override;
     sk_sp<SkSpecialImage> makeSpecial(const SkImage*) override;
     sk_sp<SkSpecialImage> snapSpecial() override;
+    void setImmutable() override { fBitmap.setImmutable(); }
 
     ///////////////////////////////////////////////////////////////////////////
 

gfx/skia/skia/src/core/SkCanvas.cpp

@@ -1195,6 +1195,7 @@ void SkCanvas::internalRestore() {
     if (layer) {
         if (fMCRec) {
             const SkIPoint& origin = layer->fDevice->getOrigin();
+            layer->fDevice->setImmutable();
             this->internalDrawDevice(layer->fDevice.get(), origin.x(), origin.y(),
                                      layer->fPaint.get(),
                                      layer->fClipImage.get(), layer->fClipMatrix);

gfx/skia/skia/src/core/SkDevice.h

@@ -271,6 +271,7 @@ protected:
     virtual sk_sp<SkSpecialImage> makeSpecial(const SkBitmap&);
     virtual sk_sp<SkSpecialImage> makeSpecial(const SkImage*);
     virtual sk_sp<SkSpecialImage> snapSpecial();
+    virtual void setImmutable() {}
 
     bool readPixels(const SkPixmap&, int x, int y);