add more checks for computing clamp counts, remove dead code

src/effects/gradients/SkLinearGradient.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkLinearGradient.h"
 
 static inline int repeat_bits(int x, const int bits) {
@@ skipping 131 matching lines @@
     SkPMColor dlerp = SkFastFourByteInterp(cache[index1], cache[index0], remainder);
     sk_memset32_dither(dstC, lerp, dlerp, count);
 }
 
 void shadeSpan_linear_clamp(TileProc proc, SkGradFixed dx, SkGradFixed fx,
                             SkPMColor* SK_RESTRICT dstC,
                             const SkPMColor* SK_RESTRICT cache,
                             int toggle, int count) {
     SkClampRange range;
     range.init(fx, dx, count, 0, SkGradientShaderBase::kCache32Count - 1);
+    range.validate(count);
 
     if ((count = range.fCount0) > 0) {
         sk_memset32_dither(dstC,
             cache[toggle + range.fV0],
             cache[next_dither_toggle(toggle) + range.fV0],
             count);
         dstC += count;
     }
     if ((count = range.fCount1) > 0) {
         int unroll = count >> 3;
@@ skipping 163 matching lines @@
     dither_memset16(dstC, cache[toggle + fi],
         cache[next_dither_toggle16(toggle) + fi], count);
 }
 
 void shadeSpan16_linear_clamp(TileProc proc, SkGradFixed dx, SkGradFixed fx,
                               uint16_t* SK_RESTRICT dstC,
                               const uint16_t* SK_RESTRICT cache,
                               int toggle, int count) {
     SkClampRange range;
     range.init(fx, dx, count, 0, SkGradientShaderBase::kCache32Count - 1);
+    range.validate(count);
 
     if ((count = range.fCount0) > 0) {
         dither_memset16(dstC,
             cache[toggle + range.fV0],
             cache[next_dither_toggle16(toggle) + range.fV0],
             count);
         dstC += count;
     }
     if ((count = range.fCount1) > 0) {
         int unroll = count >> 3;
@@ skipping 259 matching lines @@
     str->append("SkLinearGradient (");
 
     str->appendf("start: (%f, %f)", fStart.fX, fStart.fY);
     str->appendf(" end: (%f, %f) ", fEnd.fX, fEnd.fY);
 
     this->INHERITED::toString(str);
 
     str->append(")");
 }
 #endif