Implement approx-match support in image filter saveLayer() offscreen.

src/gpu/effects/GrMatrixConvolutionEffect.cpp

Index: src/gpu/effects/GrMatrixConvolutionEffect.cpp
diff --git a/src/gpu/effects/GrMatrixConvolutionEffect.cpp b/src/gpu/effects/GrMatrixConvolutionEffect.cpp
index cd6d7c1f862b70e699b5c5ad8d92583602dd0731..0b0a8af1944bc49d8c1824f2b23f1ddf7378ae48 100644
--- a/src/gpu/effects/GrMatrixConvolutionEffect.cpp
+++ b/src/gpu/effects/GrMatrixConvolutionEffect.cpp
@@ -90,6 +90,7 @@ void GrGLMatrixConvolutionEffect::emitCode(GrGLFPBuilder* builder,
             fDomain.sampleTexture(fsBuilder, domain, "c", coord, samplers[0]);
             if (!fConvolveAlpha) {
                 fsBuilder->codeAppend("c.rgb /= c.a;");
+                fsBuilder->codeAppend("c.rgb = clamp(c.rgb, 0.0, 1.0);");
             }
             fsBuilder->codeAppend("sum += c * k;");
         }
@@ -152,7 +153,7 @@ GrMatrixConvolutionEffect::GrMatrixConvolutionEffect(GrTexture* texture,
     fGain(SkScalarToFloat(gain)),
     fBias(SkScalarToFloat(bias) / 255.0f),
     fConvolveAlpha(convolveAlpha),
-    fDomain(GrTextureDomain::MakeTexelDomain(texture, bounds), tileMode) {
+    fDomain(GrTextureDomain::MakeTexelDomainForMode(texture, bounds, tileMode), tileMode) {
     this->initClassID<GrMatrixConvolutionEffect>();
     for (int i = 0; i < kernelSize.width() * kernelSize.height(); i++) {
         fKernel[i] = SkScalarToFloat(kernel[i]);