Fix 4444 on Vulkan devices who don't support RGBA_4444

src/gpu/GrGpu.cpp

Index: src/gpu/GrGpu.cpp
diff --git a/src/gpu/GrGpu.cpp b/src/gpu/GrGpu.cpp
index 7199b4d97694c62ba0555acf0a1b65939474459f..ea86e3a2fc8e0101c90207078f26d31938f53ef9 100644
--- a/src/gpu/GrGpu.cpp
+++ b/src/gpu/GrGpu.cpp
@@ -277,6 +277,12 @@ bool GrGpu::getReadPixelsInfo(GrSurface* srcSurface, int width, int height, size
         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;