add asAShadowBlur for android to drawlooper

src/effects/SkLayerDrawLooper.cpp

Index: src/effects/SkLayerDrawLooper.cpp
diff --git a/src/effects/SkLayerDrawLooper.cpp b/src/effects/SkLayerDrawLooper.cpp
index fa590d2d3fc7c1f9945abe409227b058ae68e93d..7c471c261487ce65dae303e366b21a68f53995f0 100644
--- a/src/effects/SkLayerDrawLooper.cpp
+++ b/src/effects/SkLayerDrawLooper.cpp
@@ -153,6 +153,49 @@ bool SkLayerDrawLooper::LayerDrawLooperContext::next(SkCanvas* canvas,
     return true;
 }
 
+bool SkLayerDrawLooper::asABlurShadow(BlurShadowRec* bsRec) const {
+    if (fCount != 2) {
+        return false;
+    }
+    const Rec* rec = fRecs;
+
+    // 2nd layer needs to be "plain"
+    if (rec[1].fInfo.fPaintBits) {
+        return false;
+    }
+    if (SkXfermode::kDst_Mode != rec[1].fInfo.fColorMode) {
+        return false;
+    }
+    if (0 != rec[1].fInfo.fOffset.x() || 0 != rec[1].fInfo.fOffset.y()) {
+        return false;
+    }
+
+    // 1st layer needs to be just blur(maskfilter)
+    if ((rec[0].fInfo.fPaintBits & ~kMaskFilter_Bit)) {
+        return false;
+    }
+    if (SkXfermode::kSrc_Mode != rec[0].fInfo.fColorMode) {
+        return false;
+    }
+    const SkMaskFilter* mf = rec[0].fPaint.getMaskFilter();
+    if (NULL == mf) {
+        return false;
+    }
+    SkMaskFilter::BlurRec maskBlur;
+    if (!mf->asABlur(&maskBlur)) {
+        return false;
+    }
+
+    if (bsRec) {
+        bsRec->fSigma = maskBlur.fSigma;
+        bsRec->fOffset = rec[0].fInfo.fOffset;
+        bsRec->fColor = rec[0].fPaint.getColor();
+        bsRec->fStyle = maskBlur.fStyle;
+        bsRec->fQuality = maskBlur.fQuality;
+    }
+    return true;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 void SkLayerDrawLooper::flatten(SkWriteBuffer& buffer) const {