All batches do their own pipeline compare

BUG=skia:

Review URL: https://codereview.chromium.org/1242033002
diff --git a/src/gpu/GrPipeline.cpp b/src/gpu/GrPipeline.cpp
index 8c40438..c3b8e77 100644
--- a/src/gpu/GrPipeline.cpp
+++ b/src/gpu/GrPipeline.cpp
@@ -153,6 +153,11 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 bool GrPipeline::isEqual(const GrPipeline& that) const {
+    // If we point to the same pipeline, then we are necessarily equal
+    if (this == &that) {
+        return true;
+    }
+
     if (this->getRenderTarget() != that.getRenderTarget() ||
         this->fFragmentStages.count() != that.fFragmentStages.count() ||
         this->fNumColorStages != that.fNumColorStages ||