Fix uninitialized variable warning.

src/core/SkLinearBitmapPipeline.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 "SkLinearBitmapPipeline.h"
 #include "SkPM4f.h"
 
@@ skipping 159 matching lines @@
 
 namespace  {
 template <typename Stage>
 void span_fallback(Span span, Stage* stage) {
     SkPoint start;
     SkScalar length;
     int count;
     std::tie(start, length, count) = span;
     Sk4f xs{X(start)};
     Sk4f ys{Y(start)};
-    Sk4s fourDx;
+
+    // Initializing this is not needed, but some compilers can't figure this out.
+    Sk4s fourDx{0.0f};
     if (count > 1) {
         SkScalar dx = length / (count - 1);
         xs = xs + Sk4f{0.0f, 1.0f, 2.0f, 3.0f} * dx;
         // Only used if count is >= 4.
         fourDx = Sk4f{4.0f * dx};
     }
 
     while (count >= 4) {
         stage->pointList4(xs, ys);
         xs = xs + fourDx;
@@ skipping 741 matching lines @@
 
 void SkLinearBitmapPipeline::shadeSpan4f(int x, int y, SkPM4f* dst, int count) {
     SkASSERT(count > 0);
     fPixelStage->setDestination(dst);
     // The count and length arguments start out in a precise relation in order to keep the
     // math correct through the different stages. Count is the number of pixel to produce.
     // Since the code samples at pixel centers, length is the distance from the center of the
     // first pixel to the center of the last pixel. This implies that length is count-1.
     fFirstStage->pointSpan(Span{SkPoint{x + 0.5f, y + 0.5f}, count - 1.0f, count});
 }