Enhance AudioSplicer to crossfade marked splice frames.

media/base/vector_math.cc

Index: media/base/vector_math.cc
diff --git a/media/base/vector_math.cc b/media/base/vector_math.cc
index 32584f5cf64ad2a1ecf400cbccd8f9341851cfa4..6152204ff39f3c223fe10c6901c417e0c288fe1c 100644
--- a/media/base/vector_math.cc
+++ b/media/base/vector_math.cc
@@ -88,6 +88,13 @@ void FMUL_C(const float src[], float scale, int len, float dest[]) {
     dest[i] = src[i] * scale;
 }
 
+void Crossfade(const float src[], int len, float dest[]) {
+  float cf_ratio = 0;
+  const float cf_increment = 1.0f / len;
+  for (int i = 0; i < len; ++i, cf_ratio += cf_increment)
+    dest[i] = (1.0f - cf_ratio) * src[i] + cf_ratio * dest[i];
+}
+
 std::pair<float, float> EWMAAndMaxPower(
     float initial_value, const float src[], int len, float smoothing_factor) {
   // Ensure |src| is 16-byte aligned.