Implement color filter as GrGLEffect

src/gpu/GrContext.cpp

Index: src/gpu/GrContext.cpp
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index 91e8286eb5f67eb35e0c9088ed933f0d9aa1d006..df6bf9866db9d881bfcb99d804163389efc0ad36 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -1615,7 +1615,7 @@ GrDrawTarget* GrContext::prepareToDraw(const GrPaint* paint,
                                        AutoCheckFlush* acf) {
     // All users of this draw state should be freeing up all effects when they're done.
     // Otherwise effects that own resources may keep those resources alive indefinitely.
-    SkASSERT(0 == fDrawState->numColorStages() && 0 == fDrawState->numCoverageStages());
+    SkASSERT(0 == fDrawState->totalStageCount());
 
     if (kNo_BufferedDraw == buffered && kYes_BufferedDraw == fLastDrawWasBuffered) {
         fDrawBuffer->flush();