Disable runtime feature CompositeOpaqueFixedPosition

The feature caused performance regression on low dpi devices when a
fix positioned element contains too many children.

Temporarily disble it to unblock Stable release. Will address it through
https://crbug.com/816937.

Bug: 814673
Change-Id: I6f0fea7d6b61f572b4d8da4e54c34d63cc5bc2f1
Reviewed-on: https://chromium-review.googlesource.com/939585
Commit-Queue: Yi Gu <yigu@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#539552}(cherry picked from commit fc95fed8a9e4cadd5842241b0bb93a9991ff0021)
Reviewed-on: https://chromium-review.googlesource.com/939653
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/branch-heads/3325@{#612}
Cr-Branched-From: bc084a8b5afa3744a74927344e304c02ae54189f-refs/heads/master@{#530369}
diff --git a/content/child/runtime_features.cc b/content/child/runtime_features.cc
index 964f02b..97d5278 100644
--- a/content/child/runtime_features.cc
+++ b/content/child/runtime_features.cc
@@ -302,9 +302,9 @@
   if (base::FeatureList::IsEnabled(features::kGamepadExtensions))
     WebRuntimeFeatures::EnableGamepadExtensions(true);
 
-  if (!base::FeatureList::IsEnabled(features::kCompositeOpaqueFixedPosition))
+  if (base::FeatureList::IsEnabled(features::kCompositeOpaqueFixedPosition))
     WebRuntimeFeatures::EnableFeatureFromString("CompositeOpaqueFixedPosition",
-                                                false);
+                                                true);
 
   if (!base::FeatureList::IsEnabled(features::kCompositeOpaqueScrollers))
     WebRuntimeFeatures::EnableFeatureFromString("CompositeOpaqueScrollers",
diff --git a/content/public/common/content_features.cc b/content/public/common/content_features.cc
index cf9b28c..e74d860 100644
--- a/content/public/common/content_features.cc
+++ b/content/public/common/content_features.cc
@@ -73,7 +73,7 @@
 // Enables the compositing of fixed position content that is opaque and can
 // preserve LCD text.
 const base::Feature kCompositeOpaqueFixedPosition{
-    "CompositeOpaqueFixedPosition", base::FEATURE_ENABLED_BY_DEFAULT};
+    "CompositeOpaqueFixedPosition", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables the compositing of scrolling content that supports painting the
 // background with the foreground, such that LCD text will still be enabled.