add a GM to demo the blend bug

gm/blend.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+
+DEF_SIMPLE_GM(blend, canvas, 300, 100) {
+    SkPaint p;
+
+    // All three of these blocks should be the same color.
+    canvas->save();
+        canvas->scale(100,100);
+
+        p.setColor(SK_ColorRED);
+        canvas->drawRect(SkRect::MakeXYWH(0,0,1,1), p);
+        p.setColor(0xFC008000);
+        canvas->drawRect(SkRect::MakeXYWH(0,0,1,1), p);
+
+        p.setColor(SK_ColorRED);
+        canvas->drawRect(SkRect::MakeXYWH(1,0,1,1), p);
+        canvas->saveLayer(NULL, NULL);
+            p.setColor(0xFC008000);
+            canvas->drawRect(SkRect::MakeXYWH(1,0,1,1), p);
+        canvas->restore();
+
+        p.setColor(SK_ColorRED);
+        canvas->drawRect(SkRect::MakeXYWH(2,0,1,1), p);
+        canvas->saveLayerAlpha(NULL, 0xFC);
+            p.setColor(0xFF008000);
+            canvas->drawRect(SkRect::MakeXYWH(2,0,1,1), p);
+        canvas->restore();
+    canvas->restore();
+
+    // Print out the colors in each block (if we're looking at 8888 raster).
+    if (canvas->imageInfo().colorType() == kN32_SkColorType) {
+        if (const SkPMColor* px = (const SkPMColor*)canvas->peekPixels(NULL, NULL)) {
+            p.setColor(SK_ColorWHITE);
+            for (int i = 0; i < 3; i++) {
+                SkPMColor c = px[i * 100];
+                SkString text = SkStringPrintf("0x%08x", c);
+                canvas->drawText(text.c_str(), text.size(), i * 100.0f + 20.0f, 50.0f, p);
+            }
+        }
+    }
+}