fix slowness of getImageData() for CanvasRenderingContext2D in linux due to un-optimized format for…

src/gpu/gl/GrGpuGL.cpp

Index: src/gpu/gl/GrGpuGL.cpp
diff --git a/src/gpu/gl/GrGpuGL.cpp b/src/gpu/gl/GrGpuGL.cpp
index 035ef3bb1bf43c99d5d80552cf16c1bc317d959c..aa8e9c1531ef7ca515812791cfcea3a831f985ea 100644
--- a/src/gpu/gl/GrGpuGL.cpp
+++ b/src/gpu/gl/GrGpuGL.cpp
@@ -266,21 +266,24 @@ void GrGpuGL::fillInConfigRenderableTable() {
 }
 
 namespace {
-GrPixelConfig preferred_pixel_ops_config(GrPixelConfig config) {
+GrPixelConfig preferred_pixel_ops_config(GrPixelConfig config, GrPixelConfig targetConfig) {
     if (GR_GL_RGBA_8888_PIXEL_OPS_SLOW && kRGBA_8888_GrPixelConfig == config) {
         return kBGRA_8888_GrPixelConfig;
+    } else if (config == targetConfig
+               || (GrBytesPerPixel(config) == 4 && GrPixelConfigSwapRAndB(config) == targetConfig)) {
+        return targetConfig;
     } else {
         return config;
     }
 }
 }
 
-GrPixelConfig GrGpuGL::preferredReadPixelsConfig(GrPixelConfig config) const {
-    return preferred_pixel_ops_config(config);
+GrPixelConfig GrGpuGL::preferredReadPixelsConfig(GrPixelConfig readConfig, GrPixelConfig targetConfig) const {
+    return preferred_pixel_ops_config(readConfig, targetConfig);
 }
 
-GrPixelConfig GrGpuGL::preferredWritePixelsConfig(GrPixelConfig config) const {
-    return preferred_pixel_ops_config(config);
+GrPixelConfig GrGpuGL::preferredWritePixelsConfig(GrPixelConfig writeConfig, GrPixelConfig targetConfig) const {
+    return preferred_pixel_ops_config(writeConfig, targetConfig);
 }
 
 bool GrGpuGL::canWriteTexturePixels(const GrTexture* texture, GrPixelConfig srcConfig) const {