Bug 1378375 - Kill switch preference for image network request prioritization according layout position. r=tnikkel

gfx/thebes/gfxPrefs.h

@@ -501,6 +501,7 @@ private:
   DECL_GFX_PREF(Live, "image.decode-immediately.enabled",      ImageDecodeImmediatelyEnabled, bool, false);
   DECL_GFX_PREF(Live, "image.downscale-during-decode.enabled", ImageDownscaleDuringDecodeEnabled, bool, true);
   DECL_GFX_PREF(Live, "image.infer-src-animation.threshold-ms", ImageInferSrcAnimationThresholdMS, uint32_t, 2000);
+  DECL_GFX_PREF(Live, "image.layout_network_priority",         ImageLayoutNetworkPriority, bool, true);
   DECL_GFX_PREF(Once, "image.mem.decode_bytes_at_a_time",      ImageMemDecodeBytesAtATime, uint32_t, 200000);
   DECL_GFX_PREF(Live, "image.mem.discardable",                 ImageMemDiscardable, bool, false);
   DECL_GFX_PREF(Once, "image.mem.animated.discardable",        ImageMemAnimatedDiscardable, bool, false);

image/imgRequest.cpp

@@ -558,6 +558,10 @@ imgRequest::AdjustPriorityInternal(int32_t aDelta)
 void
 imgRequest::BoostPriority(uint32_t aCategory)
 {
+  if (!gfxPrefs::ImageLayoutNetworkPriority()) {
+    return;
+  }
+
   uint32_t newRequestedCategory =
     (mBoostCategoriesRequested & aCategory) ^ aCategory;
   if (!newRequestedCategory) {

modules/libpref/init/all.js

@@ -4604,6 +4604,10 @@ pref("image.http.accept", "*/*");
 // disable.
 pref("image.infer-src-animation.threshold-ms", 2000);
 
+// Whether the network request priority should be adjusted according
+// the layout and view frame position of each particular image.
+pref("image.layout_network_priority", true);
+
 //
 // Image memory management prefs
 //