Revert "ResourceLoadScheduler: enabled the feature by default"

This reverts commit e02bb35e.

Why? Previous-step cl/193316519 is rolled back as this feature breaks working
sites, and further refinement is necessary before it should be enabled by
default. See https://crbug.com/729954#c26 onwards.

Bug: 729954,837771
Change-Id: I806364dc9a5812a0e57f76f4a3db02e6803a8d5f
Reviewed-on: https://chromium-review.googlesource.com/1042535Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Ami Fischman <fischman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555776}

content/public/common/content_features.cc

@@ -313,7 +313,7 @@ const base::Feature kResamplingInputEvents{"ResamplingInputEvents",
 
 // Loading Dispatcher v0 support with ResourceLoadScheduler (crbug.com/729954).
 const base::Feature kResourceLoadScheduler{"ResourceLoadScheduler",
-                                           base::FEATURE_ENABLED_BY_DEFAULT};
+                                           base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Use common overflow scroll mechanism for frames. See http://crbug.com/417782.
 const base::Feature kRootLayerScrolling{"RootLayerScrolling",

third_party/blink/renderer/platform/loader/fetch/resource_load_scheduler.cc

@@ -29,11 +29,7 @@ const char kOutstandingLimitForBackgroundMainFrameName[] = "bg_limit";
 const char kOutstandingLimitForBackgroundSubFrameName[] = "bg_sub_limit";
 
 // Field trial default parameters.
-// Note: Giving smaller sub-frame threshold seems to work better for improving
-// foreground loading performance, while setting it to 1u easily breaks some
-// services that have one long-polling request, and needs other resources.
-constexpr size_t kOutstandingLimitForBackgroundMainFrameDefault = 3u;
-constexpr size_t kOutstandingLimitForBackgroundSubFrameDefault = 2u;
+constexpr size_t kOutstandingLimitForBackgroundFrameDefault = 16u;
 
 // Maximum request count that request count metrics assume.
 constexpr base::HistogramBase::Sample kMaximumReportSize10K = 10000;
@@ -99,14 +95,18 @@ size_t GetOutstandingThrottledLimit(FetchContext* context) {
   if (!RuntimeEnabledFeatures::ResourceLoadSchedulerEnabled())
     return ResourceLoadScheduler::kOutstandingUnlimited;
 
-  static size_t main_frame_limit = GetFieldTrialUint32Param(
+  uint32_t main_frame_limit = GetFieldTrialUint32Param(
       kResourceLoadSchedulerTrial, kOutstandingLimitForBackgroundMainFrameName,
-      kOutstandingLimitForBackgroundMainFrameDefault);
-  static size_t sub_frame_limit = GetFieldTrialUint32Param(
-      kResourceLoadSchedulerTrial, kOutstandingLimitForBackgroundSubFrameName,
-      kOutstandingLimitForBackgroundSubFrameDefault);
-
-  return context->IsMainFrame() ? main_frame_limit : sub_frame_limit;
+      kOutstandingLimitForBackgroundFrameDefault);
+  if (context->IsMainFrame())
+    return main_frame_limit;
+
+  // We do not have a fixed default limit for sub-frames, but use the limit for
+  // the main frame so that it works as how previous versions that haven't
+  // consider sub-frames' specific limit work.
+  return GetFieldTrialUint32Param(kResourceLoadSchedulerTrial,
+                                  kOutstandingLimitForBackgroundSubFrameName,
+                                  main_frame_limit);
 }
 
 int TakeWholeKilobytes(int64_t& bytes) {