Flush the pipe in skiaserve when we switch to GPU

tools/skiaserve/Request.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Request.h"
 
 #include "png.h"
@@ skipping 159 matching lines @@
                                                     &props);
     return surface;
 }
 
 bool Request::enableGPU(bool enable) {    
     if (enable) {
         SkSurface* surface = this->createGPUSurface();
         if (surface) {
             fSurface.reset(surface);
             fGPUEnabled = true;
+
+            // When we switch to GPU, there seems to be some mystery draws in the canvas.  So we
+            // draw once to flush the pipe
+            // TODO understand what is actually happening here
+            fDebugCanvas->drawTo(this->getCanvas(), this->getLastOp());
+            this->getCanvas()->flush();
+
             return true;
         }
         return false;
     }
     fSurface.reset(this->createCPUSurface());
     fGPUEnabled = false;
     return true;
 } 
 
 bool Request::initPictureFromStream(SkStream* stream) {
@@ skipping 67 matching lines @@
     canvas->flush();
     SkAutoTDelete<SkBitmap> bitmap(this->getBitmapFromCanvas(canvas));
     SkASSERT(bitmap);
     bitmap->lockPixels();
     uint8_t* start = ((uint8_t*) bitmap->getPixels()) + (y * bitmap->width() + x) * 4;
     SkColor result = SkColorSetARGB(start[3], start[0], start[1], start[2]);
     bitmap->unlockPixels();
     return result;
 }