Bug 930535. Enable image visibility on b2g inside browser elements. r=mats

b2g/app/b2g.js

@@ -728,6 +728,7 @@ pref("font.size.inflation.disabledInMasterProcess", true);
 pref("memory.free_dirty_pages", true);
 
 pref("layout.imagevisibility.enabled", false);
+pref("layout.imagevisibility.enabled_for_browser_elements_only", true);
 pref("layout.imagevisibility.numscrollportwidths", 1);
 pref("layout.imagevisibility.numscrollportheights", 1);
 

layout/base/nsPresShell.cpp

@@ -5383,16 +5383,22 @@ bool
 PresShell::AssumeAllImagesVisible()
 {
   static bool sImageVisibilityEnabled = true;
+  static bool sImageVisibilityEnabledForBrowserElementsOnly = false;
   static bool sImageVisibilityPrefCached = false;
 
   if (!sImageVisibilityPrefCached) {
     Preferences::AddBoolVarCache(&sImageVisibilityEnabled,
-                                 "layout.imagevisibility.enabled", true);
+      "layout.imagevisibility.enabled", true);
+    Preferences::AddBoolVarCache(&sImageVisibilityEnabledForBrowserElementsOnly,
+      "layout.imagevisibility.enabled_for_browser_elements_only", false);
     sImageVisibilityPrefCached = true;
   }
 
-  if (!sImageVisibilityEnabled || !mPresContext || !mDocument)
+  if ((!sImageVisibilityEnabled &&
+       !sImageVisibilityEnabledForBrowserElementsOnly) ||
+      !mPresContext || !mDocument) {
     return true;
+  }
 
   // We assume all images are visible in print, print preview, chrome, xul, and
   // resource docs and don't keep track of them.
@@ -5404,6 +5410,15 @@ PresShell::AssumeAllImagesVisible()
     return true;
   }
 
+  if (!sImageVisibilityEnabled &&
+      sImageVisibilityEnabledForBrowserElementsOnly) {
+    nsCOMPtr<nsISupports> container = mPresContext->GetContainer();
+    nsCOMPtr<nsIDocShell> docshell(do_QueryInterface(container));
+    if (!docshell || !docshell->GetIsInBrowserElement()) {
+      return true;
+    }
+  }
+
   return false;
 }
 

modules/libpref/src/init/all.js

@@ -550,7 +550,13 @@ pref("nglayout.debug.paint_flashing_chrome", false);
 // BasicLayers (other layer managers always update the entire widget area)
 pref("nglayout.debug.widget_update_flashing", false);
 
+// Whether image visibility is enabled globally (ie we will try to unlock images
+// that are not visible).
 pref("layout.imagevisibility.enabled", true);
+// Whether image visibility is enabled in documents that are within a browser
+// element as defined by nsDocShell::FrameType and GetInheritedFrameType. This
+// pref only has an effect if layout.imagevisibility.enabled is false.
+pref("layout.imagevisibility.enabled_for_browser_elements_only", false);
 pref("layout.imagevisibility.numscrollportwidths", 0);
 pref("layout.imagevisibility.numscrollportheights", 1);