just add SkLiteDL::empty()

src/core/SkLiteDL.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvas.h"
 #include "SkData.h"
 #include "SkImageFilter.h"
@@ skipping 737 matching lines @@
 #undef M
 
 void SkLiteDL::onDraw        (SkCanvas* canvas) { this->map(draw_fns, canvas); }
 void SkLiteDL::optimizeFor   (GrContext* ctx)   { this->map(optimize_for_fns, ctx); }
 void SkLiteDL::makeThreadsafe()                 { this->map(make_threadsafe_fns); }
 
 SkRect SkLiteDL::onGetBounds() {
     return fBounds;
 }
 
+bool SkLiteDL::empty() const {
+    return fUsed == 0;
+}
+
 #if !defined(SK_LITEDL_USES)
     #define  SK_LITEDL_USES 16
 #endif
 
 SkLiteDL:: SkLiteDL() : fUsed(0), fReserved(0), fUsesRemaining(SK_LITEDL_USES) {}
 SkLiteDL::~SkLiteDL() {}
 
 // If you're tempted to make this lock free, please don't forget about ABA.
 static SkSpinlock gFreeStackLock;
 static SkLiteDL*  gFreeStack = nullptr;
@@ skipping 37 matching lines @@
 }
 
 void SkLiteDL::PurgeFreelist() {
     SkAutoMutexAcquire lock(gFreeStackLock);
     while (gFreeStack) {
         SkLiteDL* top = gFreeStack;
         gFreeStack = gFreeStack->fNext;
         delete top;   // Calling unref() here would just put it back on the list!
     }
 }