Read saturation boost from a persistent property

We use a persisten property because Android's various settings
stores are not available early enough to avoid a color change
during the boot animation.

Bug: 62238038
Test: Manual
Change-Id: I905435efe89b5e1c85fc8a396b7888de5c318a18
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 78579a5..13472df 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -225,6 +225,9 @@
     property_get("ro.sf.disable_triple_buffer", value, "1");
     mLayerTripleBufferingDisabled = atoi(value);
     ALOGI_IF(mLayerTripleBufferingDisabled, "Disabling Triple Buffering");
+
+    property_get("persist.sys.sf.color_saturation", value, "1.0");
+    mSaturation = atof(value);
 }
 
 void SurfaceFlinger::onFirstRef()