some basic speed ups for SkRasterPipeline::append()

The new bench demos the speedup:
    SkRasterPipelineReuse_…
    …full 1x  …some 1.8x  …none 5.22x

Change-Id: I5e51fb4316ae04558710ce62560850584ccb4aea
Reviewed-on: https://skia-review.googlesource.com/17449
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/src/core/SkRasterPipeline.cpp b/src/core/SkRasterPipeline.cpp
index d307bdd118..ab404446e0 100644
--- a/src/core/SkRasterPipeline.cpp
+++ b/src/core/SkRasterPipeline.cpp
@@ -7,7 +7,13 @@
 
 #include "SkRasterPipeline.h"
 
-SkRasterPipeline::SkRasterPipeline() {}
+SkRasterPipeline::SkRasterPipeline(int size_hint) {
+    fStages.reserve(size_hint);
+}
+
+void SkRasterPipeline::rewind() {
+    fStages.clear();
+}
 
 void SkRasterPipeline::append(StockStage stage, void* ctx) {
     SkASSERT(stage != from_srgb);