Add fExternalFormatForTexImage to GrGLGpu::ConfigEntry. Use it in GrGLGpu::uploadTexData.

src/gpu/gl/GrGLGpu.h

Index: src/gpu/gl/GrGLGpu.h
diff --git a/src/gpu/gl/GrGLGpu.h b/src/gpu/gl/GrGLGpu.h
index 4f3b37ee9dfac7de1612bf91b7e50d48d4b8c52b..e3b590f017b000f759e959bc323eb6f76ab1994e 100644
--- a/src/gpu/gl/GrGLGpu.h
+++ b/src/gpu/gl/GrGLGpu.h
@@ -550,6 +550,10 @@ private:
         GrGLenum fExternalFormat;
         GrGLenum fExternalType;
 
+        // The <format> parameter to use for glTexImage and glTexSubImage.
+        // This is usually the same as fExternalFormat except for kSRGBA on some GL contexts.
+        GrGLenum fExternalFormatForTexImage;
+
         // Index into GrGLCaps's list of stencil formats. Support is determined experimentally and
         // lazily.
         int      fStencilFormatIndex;