add virtuals to optimize composing colorfilters

src/core/SkColorFilter.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkColorFilter.h"
 #include "SkReadBuffer.h"
 #include "SkString.h"
@@ skipping 86 matching lines @@
 
     typedef SkColorFilter INHERITED;
 };
 
 SkFlattenable* SkComposeColorFilter::CreateProc(SkReadBuffer& buffer) {
     SkAutoTUnref<SkColorFilter> outer(buffer.readColorFilter());
     SkAutoTUnref<SkColorFilter> inner(buffer.readColorFilter());
     return CreateComposeFilter(outer, inner);
 }
 
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
 SkColorFilter* SkColorFilter::CreateComposeFilter(SkColorFilter* outer, SkColorFilter* inner) {
     if (!outer) {
         return SkSafeRef(inner);
     }
     if (!inner) {
         return SkSafeRef(outer);
     }
-    return SkNEW_ARGS(SkComposeColorFilter, (outer, inner));
+
+    // Give the subclass a shot at a more optimal composition...
+    SkColorFilter* composition = outer->newComposed(inner);
+    if (NULL == composition) {
+        composition = SkNEW_ARGS(SkComposeColorFilter, (outer, inner));
+    }
+    return composition;
 }
 
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkColorFilter)
 SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkComposeColorFilter)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END