Fix some GPU image filter code to preserve precision and color space

src/gpu/SkGr.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 "SkGr.h"
 #include "SkGrPriv.h"
@@ skipping 490 matching lines @@
             break;
         default:
             return false;
     }
     if (ctOut) {
         *ctOut = ct;
     }
     return true;
 }
 
+GrPixelConfig GrRenderableConfigForColorSpace(SkColorSpace* colorSpace) {
+    if (!colorSpace) {
+        return kRGBA_8888_GrPixelConfig;
+    } else if (colorSpace->gammaIsLinear()) {
+        return kRGBA_half_GrPixelConfig;
+    } else if (colorSpace->gammaCloseToSRGB()) {
+        return kSRGBA_8888_GrPixelConfig;
+    } else {
+        SkDEBUGFAIL("No renderable config exists for color space with strange gamma");
+        return kUnknown_GrPixelConfig;
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////////////////////
 
 static inline bool blend_requires_shader(const SkXfermode::Mode mode, bool primitiveIsSrc) {
     if (primitiveIsSrc) {
         return SkXfermode::kSrc_Mode != mode;
     } else {
         return SkXfermode::kDst_Mode != mode;
     }
 }
 
@@ skipping 253 matching lines @@
             SkErrorInternals::SetError( kInvalidPaint_SkError,
                                         "Sorry, I don't understand the filtering "
                                         "mode you asked for.  Falling back to "
                                         "MIPMaps.");
             textureFilterMode = GrTextureParams::kMipMap_FilterMode;
             break;
 
     }
     return textureFilterMode;
 }