Fix 4444 on Vulkan devices who don't support RGBA_4444

src/gpu/GrGpu.cpp

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrGpu.h"
 
@@ skipping 259 matching lines @@
                               ReadPixelTempDrawInfo* tempDrawInfo) {
     SkASSERT(drawPreference);
     SkASSERT(tempDrawInfo);
     SkASSERT(kGpuPrefersDraw_DrawPreference != *drawPreference);
 
     // We currently do not support reading into a compressed buffer
     if (GrPixelConfigIsCompressed(readConfig)) {
         return false;
     }
 
+    // We currently do not support reading into the pack formats 565 or 4444 as they are not
+    // required to be renderable formats on all backends.

[bsalomon, 2016/08/15 16:24:08]

I don't know that the fundamental problem is renderability. ES 3.2 does require
they're renderable, but it still doesn't guarantee support that they can be
read. The real problem is that you can't use them as a read back format.

[egdaniel, 2016/08/15 17:03:01]

Done.

+    if (kRGB_565_GrPixelConfig == readConfig || kRGBA_4444_GrPixelConfig == readConfig) {
+        return false;
+    }
+
     if (!this->onGetReadPixelsInfo(srcSurface, width, height, rowBytes, readConfig, drawPreference,
                                    tempDrawInfo)) {
         return false;
     }
 
     // Check to see if we're going to request that the caller draw when drawing is not possible.
     if (!srcSurface->asTexture() ||
         !this->caps()->isConfigRenderable(tempDrawInfo->fTempSurfaceDesc.fConfig, false)) {
         // If we don't have a fallback to a straight read then fail.
         if (kRequireDraw_DrawPreference == *drawPreference) {
@@ skipping 193 matching lines @@
         // This doesn't have geometric meaning. We just need to define an ordering for std::map.
         if (a[i].x() != b[i].x()) {
             return a[i].x() < b[i].x();
         }
         if (a[i].y() != b[i].y()) {
             return a[i].y() < b[i].y();
         }
     }
     return false; // Equal.
 }