helium/core: enable autoscroll on linux by default, add a flag

closes #233

patches/helium/core/add-middle-click-autoscroll-flag.patch

@@ -0,0 +1,64 @@
+--- a/chrome/browser/helium_flag_choices.h
++++ b/chrome/browser/helium_flag_choices.h
+@@ -29,6 +29,7 @@ namespace helium {
+   constexpr const char kDisableEchCommandLine[] = "disable-ech";
+   constexpr const char kCanvasNoiseCommandLine[] = "fingerprinting-canvas-noise";
+   constexpr const char kAudioContextJitterCommandLine[] = "fingerprinting-audio-context-jitter";
++  constexpr const char kMiddleClickAutoscrollCommandLine[] = "middle-click-autoscroll";
+ 
+ }  // namespace helium
+ 
+--- a/chrome/browser/helium_flag_entries.h
++++ b/chrome/browser/helium_flag_entries.h
+@@ -24,4 +24,8 @@
+      "Audio Context fingerprint deception",
+      "Adds small random jitter (±0.01%) to audio data to prevent fingerprinting. Helium flag.",
+      kOsAll, FEATURE_VALUE_TYPE(blink::features::kAudioContextJitter)},
++    {helium::kMiddleClickAutoscrollCommandLine,
++     "Middle Click Autoscroll",
++     "Enables autoscroll on middle click. Helium flag, Chromium feature.",
++     kOsDesktop, FEATURE_VALUE_TYPE(blink::features::kHeliumMiddleClickAutoscroll)},
+ #endif  /* CHROME_BROWSER_HELIUM_FLAG_ENTRIES_H_ */
+--- a/third_party/blink/public/common/features.h
++++ b/third_party/blink/public/common/features.h
+@@ -23,6 +23,7 @@ namespace blink {
+ namespace features {
+ 
+ BLINK_COMMON_EXPORT BASE_DECLARE_FEATURE(kAudioContextJitter);
++BLINK_COMMON_EXPORT BASE_DECLARE_FEATURE(kHeliumMiddleClickAutoscroll);
+ 
+ BLINK_COMMON_EXPORT BASE_DECLARE_FEATURE(kDisableLinkDrag);
+ BLINK_COMMON_EXPORT BASE_DECLARE_FEATURE(kReducedSystemInfo);
+--- a/third_party/blink/common/features.cc
++++ b/third_party/blink/common/features.cc
+@@ -23,6 +23,15 @@ BASE_FEATURE(kAudioContextJitter,
+              "AudioContextJitter",
+              base::FEATURE_ENABLED_BY_DEFAULT);
+ 
++BASE_FEATURE(kHeliumMiddleClickAutoscroll,
++             "HeliumMiddleClickAutoscroll",
++#if BUILDFLAG(IS_WIN) || BUILDFLAG(IS_LINUX)
++             base::FEATURE_ENABLED_BY_DEFAULT
++#else
++             base::FEATURE_DISABLED_BY_DEFAULT
++#endif
++);
++
+ BASE_FEATURE(kDisableLinkDrag, "DisableLinkDrag", base::FEATURE_DISABLED_BY_DEFAULT);
+ BASE_FEATURE(kReducedSystemInfo, "ReducedSystemInfo", base::FEATURE_DISABLED_BY_DEFAULT);
+ BASE_FEATURE(kRemoveClientHints, "RemoveClientHints", base::FEATURE_DISABLED_BY_DEFAULT);
+--- a/third_party/blink/renderer/core/exported/web_view_impl.cc
++++ b/third_party/blink/renderer/core/exported/web_view_impl.cc
+@@ -1902,9 +1902,9 @@ void WebView::ApplyWebPreferences(const
+       prefs.default_maximum_page_scale_factor);
+ #endif
+ 
+-#if BUILDFLAG(IS_WIN)
+-  RuntimeEnabledFeatures::SetMiddleClickAutoscrollEnabled(true);
+-#endif
++  RuntimeEnabledFeatures::SetMiddleClickAutoscrollEnabled(
++    base::FeatureList::IsEnabled(features::kHeliumMiddleClickAutoscroll)
++  );
+ 
+   RuntimeEnabledFeatures::SetTranslateServiceEnabled(
+       prefs.translate_service_available);

patches/series

@@ -177,6 +177,7 @@ helium/core/disable-touch-ui.patch
 helium/core/open-new-tabs-next-to-active-tab-option.patch
 helium/core/disable-update-toast.patch
 helium/core/disable-fedcm-bubble.patch
+helium/core/add-middle-click-autoscroll-flag.patch
 
 helium/settings/move-search-suggest.patch
 helium/settings/remove-autofill.patch