Prevent division by 0 in set_luminance shader function.

cc/output/shader.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/output/shader.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
@@ skipping 786 matching lines @@
   static const std::string kFunctionLum = SHADER0(
       // clang-format on
       float luminance(vec3 color) { return dot(vec3(0.3, 0.59, 0.11), color); }
 
       vec3 set_luminance(vec3 hueSat, float alpha, vec3 lumColor) {
         float diff = luminance(lumColor - hueSat);
         vec3 outColor = hueSat + diff;
         float outLum = luminance(outColor);
         float minComp = min(min(outColor.r, outColor.g), outColor.b);
         float maxComp = max(max(outColor.r, outColor.g), outColor.b);
-        if (minComp < 0.0) {
+        if (minComp < 0.0 && outLum != minComp) {
           outColor = outLum +
                      ((outColor - vec3(outLum, outLum, outLum)) * outLum) /
                          (outLum - minComp);
         }
-        if (maxComp > alpha) {
+        if (maxComp > alpha && maxComp != outLum) {
           outColor =
               outLum +
               ((outColor - vec3(outLum, outLum, outLum)) * (alpha - outLum)) /
                   (maxComp - outLum);
         }
         return outColor;
       }
       // clang-format off
   );  // NOLINT(whitespace/parens)
 
@@ skipping 1156 matching lines @@
         vec2 coord = mod(floor(texCoord * frequency * 2.0), 2.0);
         float picker = abs(coord.x - coord.y);  // NOLINT
         gl_FragColor = mix(color1, color2, picker) * alpha;
       }
       // clang-format off
   );  // NOLINT(whitespace/parens)
   // clang-format on
 }
 
 }  // namespace cc