Add flag to make all position:fixed elements create stacking contexts

BUG=129277
TEST=none


Review URL: https://chromiumcodereview.appspot.com/10411083

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@138930 0039d316-1c4b-4281-b951-d872f2087c98

8 files changed, 26 insertions, 1 deletions

diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 2574561..f0b2503 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -5432,6 +5432,12 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_DISABLE_WEBGL_DESCRIPTION" desc="Description for the flag to disable WebGL.">
         Enabling this option prevents web applications from accessing the WebGL API.
       </message>
+      <message name="IDS_FLAGS_FIXED_POSITION_CREATES_STACKING_CONTEXT_NAME" desc="Name of the 'Fixed position creates stacking context' lab.">
+        Fixed position elements create stacking contexts.
+      </message>
+      <message name="IDS_FLAGS_FIXED_POSITION_CREATES_STACKING_CONTEXT_DESCRIPTION" desc="Description for the flag to make fixed position elements create stacking contexts.">
+        Enabling this option makes all fixed position elements create new CSS stacking contexts.
+      </message>
       <message name="IDS_FLAGS_ENABLE_HTTP_PIPELINING_NAME" desc="Title for the flag to enable HTTP pipelining">
         HTTP Pipelining
       </message>
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 9f9f038f..da85977 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -245,6 +245,13 @@ const Experiment kExperiments[] = {
     kOsAll,
     SINGLE_VALUE_TYPE(switches::kEnableBrowserPlugin)
   },
+  {
+    "fixed-position-creates-stacking-context",
+    IDS_FLAGS_FIXED_POSITION_CREATES_STACKING_CONTEXT_NAME,
+    IDS_FLAGS_FIXED_POSITION_CREATES_STACKING_CONTEXT_DESCRIPTION,
+    kOsAll,
+    SINGLE_VALUE_TYPE(switches::kFixedPositionCreatesStackingContext)
+  },
   // TODO(dspringer): When NaCl is on by default, remove this flag entry.
   {
     "enable-nacl",  // FLAGS:RECORD_UMA
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index d61e9ee..f92f107 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -574,6 +574,9 @@ WebPreferences WebContentsImpl::GetWebkitPrefs(RenderViewHost* rvh,
     prefs.apply_default_device_scale_factor_in_compositor = true;
   }
 
+  prefs.fixed_position_creates_stacking_context =
+      command_line.HasSwitch(switches::kFixedPositionCreatesStackingContext);
+
   content::GetContentClient()->browser()->OverrideWebkitPrefs(rvh, url, &prefs);
 
   return prefs;
diff --git a/content/common/view_messages.h b/content/common/view_messages.h
index 04f8c0d..e85bda1 100644
--- a/content/common/view_messages.h
+++ b/content/common/view_messages.h
@@ -211,6 +211,7 @@ IPC_STRUCT_TRAITS_BEGIN(webkit_glue::WebPreferences)
   IPC_STRUCT_TRAITS_MEMBER(default_tile_height)
   IPC_STRUCT_TRAITS_MEMBER(max_untiled_layer_width)
   IPC_STRUCT_TRAITS_MEMBER(max_untiled_layer_height)
+  IPC_STRUCT_TRAITS_MEMBER(fixed_position_creates_stacking_context)
 IPC_STRUCT_TRAITS_END()
 
 IPC_STRUCT_TRAITS_BEGIN(WebMenuItem)
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index 882da97..1905c2c 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -644,4 +644,6 @@ const char kDefaultTileHeight[]             = "default-tile-height";
 const char kMaxUntiledLayerWidth[]          = "max-untiled-layer-width";
 const char kMaxUntiledLayerHeight[]         = "max-untiled-layer-height";
 
+const char kFixedPositionCreatesStackingContext[]
+    = "fixed-position-creates-stacking-context";
 }  // namespace switches
diff --git a/content/public/common/content_switches.h b/content/public/common/content_switches.h
index 9eeaa36..31a1b11 100644
--- a/content/public/common/content_switches.h
+++ b/content/public/common/content_switches.h
@@ -187,6 +187,7 @@ extern const char kDefaultTileWidth[];
 extern const char kDefaultTileHeight[];
 extern const char kMaxUntiledLayerWidth[];
 extern const char kMaxUntiledLayerHeight[];
+CONTENT_EXPORT extern const char kFixedPositionCreatesStackingContext[];
 
 extern const char kEnableVisualWordMovement[];
 
diff --git a/webkit/glue/webpreferences.cc b/webkit/glue/webpreferences.cc
index 883da73..55740dc 100644
--- a/webkit/glue/webpreferences.cc
+++ b/webkit/glue/webpreferences.cc
@@ -110,7 +110,8 @@ WebPreferences::WebPreferences()
       default_tile_width(256),
       default_tile_height(256),
       max_untiled_layer_width(512),
-      max_untiled_layer_height(512) {
+      max_untiled_layer_height(512),
+      fixed_position_creates_stacking_context(false) {
   standard_font_family_map[kCommonScript] =
       ASCIIToUTF16("Times New Roman");
   fixed_font_family_map[kCommonScript] =
@@ -373,6 +374,9 @@ void WebPreferences::Apply(WebView* web_view) const {
   settings->setMaxUntiledLayerSize(
       WebSize(max_untiled_layer_width, max_untiled_layer_height));
 
+  settings->setFixedPositionCreatesStackingContext(
+      fixed_position_creates_stacking_context);
+
   WebNetworkStateNotifier::setOnLine(is_online);
 }
 
diff --git a/webkit/glue/webpreferences.h b/webkit/glue/webpreferences.h
index fd7c9cd..48c9881 100644
--- a/webkit/glue/webpreferences.h
+++ b/webkit/glue/webpreferences.h
@@ -127,6 +127,7 @@ struct WEBKIT_GLUE_EXPORT WebPreferences {
   int default_tile_height;
   int max_untiled_layer_width;
   int max_untiled_layer_height;
+  bool fixed_position_creates_stacking_context;
 
   // We try to keep the default values the same as the default values in
   // chrome, except for the cases where it would require lots of extra work for