Add experimental setup for MultiBufferNeverDefer.

This adds the field trial config and the WebView kill switch.

R=tmathmeyer

Bug: 41161335
Change-Id: I3bd03cdf031cca82517252165681d6e18c320872
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6426623
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Ted (Chromium) Meyer <tmathmeyer@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1442523}

android_webview/java/src/org/chromium/android_webview/common/ProductionSupportedFlagList.java

@@ -1076,6 +1076,9 @@ public final class ProductionSupportedFlagList {
                 NetworkServiceFeatures.INCREASE_COOKIE_ACCESS_CACHE_SIZE,
                 "When enabled, keep more cookies in the cache to be able to skip redundant access"
                         + " notifications."),
+        Flag.baseFeature(
+                MediaFeatures.MULTI_BUFFER_NEVER_DEFER,
+                "Controls behavior of network deferrals during media src=file playbacks."),
         // Add new commandline switches and features above. The final entry should have a
         // trailing comma for cleaner diffs.
     };

media/base/media_switches.cc

@@ -542,6 +542,14 @@ BASE_FEATURE(kMemoryPressureBasedSourceBufferGC,
              "MemoryPressureBasedSourceBufferGC",
              base::FEATURE_DISABLED_BY_DEFAULT);
 
+// Forces SuggestProviderState() to only suggest deferring when range requests
+// aren't supported. Will cause us to buffer up to preload then release the
+// loader -- creating a new one to refill beyond the preload amount. Increases
+// the number of network connections used during loading, but may prevent hangs.
+BASE_FEATURE(kMultiBufferNeverDefer,
+             "MultiBufferNeverDefer",
+             base::FEATURE_DISABLED_BY_DEFAULT);
+
 // Controls whether the Mirroring Service will fetch, analyze, and store
 // information on the quality of the session using RTCP logs.
 BASE_FEATURE(kEnableRtcpReporting,

media/base/media_switches.h

@@ -310,6 +310,7 @@ MEDIA_EXPORT BASE_DECLARE_FEATURE(kMediaLearningSmoothnessExperiment);
 MEDIA_EXPORT BASE_DECLARE_FEATURE(kMediaOptimizer);
 MEDIA_EXPORT BASE_DECLARE_FEATURE(kMediaPowerExperiment);
 MEDIA_EXPORT BASE_DECLARE_FEATURE(kMemoryPressureBasedSourceBufferGC);
+MEDIA_EXPORT BASE_DECLARE_FEATURE(kMultiBufferNeverDefer);
 MEDIA_EXPORT BASE_DECLARE_FEATURE(kOverlayFullscreenVideo);
 MEDIA_EXPORT BASE_DECLARE_FEATURE(kPauseBackgroundMutedAudio);
 #if !BUILDFLAG(IS_ANDROID)

testing/variations/fieldtrial_testing_config.json

@@ -15027,6 +15027,26 @@
             ]
         }
     ],
+    "MultiBufferNeverDefer": [
+        {
+            "platforms": [
+                "android",
+                "android_webview",
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "MultiBufferNeverDefer"
+                    ]
+                }
+            ]
+        }
+    ],
     "MultiCalendarSupport": [
         {
             "platforms": [

third_party/blink/renderer/platform/media/multi_buffer.cc

@@ -13,20 +13,13 @@
 #include "base/memory/raw_ptr.h"
 #include "base/not_fatal_until.h"
 #include "base/task/single_thread_task_runner.h"
+#include "media/base/media_switches.h"
 #include "third_party/blink/renderer/platform/scheduler/public/post_cross_thread_task.h"
 #include "third_party/blink/renderer/platform/wtf/cross_thread_functional.h"
 #include "third_party/blink/renderer/platform/wtf/functional.h"
 
 namespace blink {
 
-// Forces SuggestProviderState() to only suggest deferring when range requests
-// aren't supported. Will cause us to buffer up to preload then release the
-// loader -- creating a new one to refill beyond the preload amount. Increases
-// the number of network connections used during loading, but may prevent hangs.
-BASE_FEATURE(kMultiBufferNeverDefer,
-             "MultiBufferNeverDefer",
-             base::FEATURE_DISABLED_BY_DEFAULT);
-
 // Prune 80 blocks per 30 seconds.
 // This means a full cache will go away in ~5 minutes.
 enum {
@@ -379,7 +372,7 @@ MultiBuffer::ProviderState MultiBuffer::SuggestProviderState(
     MultiBufferBlockId previous_writer_pos =
         ClosestPreviousEntry(writer_index_, pos - 1);
     if (previous_writer_pos < previous_reader_pos) {
-      if (base::FeatureList::IsEnabled(kMultiBufferNeverDefer) &&
+      if (base::FeatureList::IsEnabled(media::kMultiBufferNeverDefer) &&
           RangeSupported()) {
         return ProviderStateDead;
       }