Fix recording of saveLayout with unusual Xfermodes.

src/core/SkRecordDraw.cpp

Index: src/core/SkRecordDraw.cpp
diff --git a/src/core/SkRecordDraw.cpp b/src/core/SkRecordDraw.cpp
index ac1e429f1227a575e27cb0342171842ac46a41b7..e1975e1fe3649e2fb372c8804251017ddd20f7c6 100644
--- a/src/core/SkRecordDraw.cpp
+++ b/src/core/SkRecordDraw.cpp
@@ -229,8 +229,43 @@ private:
     }
 
     static bool PaintMayAffectTransparentBlack(const SkPaint* paint) {
-        // FIXME: this is very conservative
-        return paint && (paint->getImageFilter() || paint->getColorFilter());
+        if (paint) {
+            // FIXME: this is very conservative
+            if (paint->getImageFilter() || paint->getColorFilter()) {
+                return true;
+            }
+
+            // Unusual Xfermodes require us to process a saved layer
+            // even with operations outisde the clip.
+            // For example, DstIn is used by masking layers.
+            // https://code.google.com/p/skia/issues/detail?id=1291
+            // https://crbug.com/401593
+            SkXfermode* xfermode = paint->getXfermode();
+            SkXfermode::Mode mode;
+            // SrcOver is ok, and is also the common case with a NULL xfermode.
+            // So we should make that the fast path and bypass the mode extraction
+            // and test.
+            if (xfermode && xfermode->asMode(&mode)) {
+                switch (mode) {
+                    // For each of the following transfer modes, if the source
+                    // alpha is zero (our transparent black), the resulting
+                    // blended alpha is not necessarily equal to the original
+                    // destination alpha.
+                    case SkXfermode::kClear_Mode:
+                    case SkXfermode::kSrc_Mode:
+                    case SkXfermode::kSrcIn_Mode:
+                    case SkXfermode::kDstIn_Mode:
+                    case SkXfermode::kSrcOut_Mode:
+                    case SkXfermode::kDstATop_Mode:
+                    case SkXfermode::kModulate_Mode:
+                        return true;
+                        break;
+                    default:
+                        break;
+                }
+            }
+        }
+        return false;
     }
 
     Bounds popSaveBlock() {