move colorshader into its own .cpp, add color4f variant

samplecode/GMSampleView.cpp

Index: samplecode/GMSampleView.cpp
diff --git a/samplecode/GMSampleView.cpp b/samplecode/GMSampleView.cpp
index 76d0c59738730dde8f841ce69c8e6b97efd94f27..80a6803148047cc848e37b3009c4bb94b2f02c38 100644
--- a/samplecode/GMSampleView.cpp
+++ b/samplecode/GMSampleView.cpp
@@ -37,11 +37,39 @@ bool GMSampleView::onEvent(const SkEvent& evt) {
     return this->INHERITED::onEvent(evt);
 }
 
+#include "SkPicture.h"
+#include "SkStream.h"
+static sk_sp<SkPicture> round_trip_serialize(SkPicture* src) {
+    SkDynamicMemoryWStream stream;
+    src->serialize(&stream);
+    SkAutoTDelete<SkStream> reader(stream.detachAsStream());
+    return SkPicture::MakeFromStream(reader);
+}
+
+#include "SkPictureRecorder.h"
 void GMSampleView::onDrawContent(SkCanvas* canvas) {
+    SkPictureRecorder recorder;
+    SkCanvas* origCanvas = canvas;
+
+    if (false) {
+        SkISize size = fGM->getISize();
+        canvas = recorder.beginRecording(SkRect::MakeIWH(size.width(), size.height()));
+    }
+
     {
         SkAutoCanvasRestore acr(canvas, fShowSize);
         fGM->drawContent(canvas);
     }
+
+    if (origCanvas != canvas) {
+        sk_sp<SkPicture> pic = recorder.finishRecordingAsPicture();
+        if (false) {
+            pic = round_trip_serialize(pic.get());
+        }
+        origCanvas->drawPicture(pic);
+        canvas = origCanvas;
+    }
+
     if (fShowSize) {
         SkISize size = fGM->getISize();
         SkRect r = SkRect::MakeWH(SkIntToScalar(size.width()),