DEPS: Update leveldatabase from 1.18 to 1.20.

third_party/leveldatabase/BUILD.gn

Index: third_party/leveldatabase/BUILD.gn
diff --git a/third_party/leveldatabase/BUILD.gn b/third_party/leveldatabase/BUILD.gn
index c8776c887c38929d645fd2f02a0c0879738f72c6..d943efac02792bb281e89064bf86ff8c925d337b 100644
--- a/third_party/leveldatabase/BUILD.gn
+++ b/third_party/leveldatabase/BUILD.gn
@@ -14,6 +14,21 @@ config("leveldatabase_config") {
   ]
 }
 
+source_set("leveldatabase_opts.sse42") {
+  sources = [
+    "src/port/port_posix_sse.cc",
+  ]
+
+  configs += [ ":leveldatabase_config" ]
+
+  if (target_cpu == "x86" || target_cpu == "x64") {
+    defines += [ "LEVELDB_PLATFORM_POSIX_SSE" ]
+    if (!is_win || is_clang) {
+      cflags = [ "-msse4.2" ]
+    }
+  }
+}
+
 static_library("leveldatabase") {
   sources = [
     "env_chromium.cc",
@@ -108,6 +123,7 @@ static_library("leveldatabase") {
   public_configs = [ ":leveldatabase_config" ]
 
   deps = [
+    ":leveldatabase_opts.sse42",
     "//base",
     "//base/third_party/dynamic_annotations",
     "//third_party/re2",