Restore SkCanvas::kPreserveLCDText_SaveLayerFlag

Will use this in Chrome to support LCDText in saveLayer/restore with
opacity.

This partly reverts https://skia-review.googlesource.com/c/skia/+/181841.

Bug: 1076019
Change-Id: Id870fb1dcc95c9b319797e936725b4447a97d1d5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/285956
Commit-Queue: Florin Malita <fmalita@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Auto-Submit: Xianzhu Wang <wangxianzhu@chromium.org>
diff --git a/RELEASE_NOTES.txt b/RELEASE_NOTES.txt
index ad63cfc..fbb8b60 100644
--- a/RELEASE_NOTES.txt
+++ b/RELEASE_NOTES.txt
@@ -8,6 +8,10 @@
 
   * <insert new release note here>
 
+  * Add back SkCanvas::kPreserveLCDText_SaveLayerFlag to indicate that saveLayer()
+    will preserve LCD-text. All text in the layer must be drawn on opaque background
+    to ensure correct rendering.
+
   * Add the new directory client_utils/ for code that is specific to a single client and
     should be considered separate from Skia proper. Move SkFrontBufferedStream into the
     subdir android/.