Add context option to disable mipmap support

This is desired for a short term memory improvement on low memory
devices.

Bug: chromium:1138979
Change-Id: I7df41a9c4d21b7a7f62b738e6358b36dd262f77d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/327345
Commit-Queue: Kyle Charbonneau <kylechar@chromium.org>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/RELEASE_NOTES.txt b/RELEASE_NOTES.txt
index a019c11..f3f13e2 100644
--- a/RELEASE_NOTES.txt
+++ b/RELEASE_NOTES.txt
@@ -9,6 +9,9 @@
 
   * <insert new release notes here>
 
+  * Add field to GrContextOptions to disable mipmap support even if the backend
+    supports it.
+
   * SkTPin() removed from public API.
 
   * Add new SkImageFilters::Blend factory function, in place of the now deprecated