Bug 290752. Don't create unnecessary level of style contexts for scrolled frames. r+sr=bzbarsky,a=asa

layout/base/nsCSSFrameConstructor.cpp

@@ -4577,6 +4577,14 @@ nsCSSFrameConstructor::ConstructRootFrame(nsIContent*     aDocElement,
                                                       rootPseudo,
                                                       viewportPseudoStyle);
   } else {
+      if (rootPseudo == nsCSSAnonBoxes::canvas) {
+        rootPseudo = nsCSSAnonBoxes::scrolledCanvas;
+      } else {
+        NS_ASSERTION(rootPseudo == nsCSSAnonBoxes::pageSequence,
+                     "Unknown root pseudo");
+        rootPseudo = nsCSSAnonBoxes::scrolledPageSequence;
+      }
+
       // Build the frame. We give it the content we are wrapping which is the document,
       // the root frame, the parent view port frame, and we should get back the new
       // frame and the scrollable view if one was created.
@@ -6280,14 +6288,7 @@ nsCSSFrameConstructor::BeginBuildingScrollFrame(nsFrameConstructorState& aState,
   aNewFrame = gfxScrollFrame;
 
   // we used the style that was passed in. So resolve another one.
-  nsRefPtr<nsStyleContext> scrollPseudoStyle;
   nsStyleSet *styleSet = mPresShell->StyleSet();
-
-  scrollPseudoStyle = styleSet->ResolvePseudoStyleFor(aContent,
-                                                      nsCSSAnonBoxes::scrolledContent,
-                                                      contentStyle);
-
-  contentStyle = scrollPseudoStyle;
   nsStyleContext* aScrolledChildStyle = styleSet->ResolvePseudoStyleFor(aContent,
                                                                         aScrolledPseudo,
                                                                         contentStyle).get();

layout/style/nsCSSAnonBoxList.h

@@ -83,6 +83,8 @@ CSS_ANON_BOX(page, ":-moz-page")
 CSS_ANON_BOX(pageContent, ":-moz-pagecontent")
 CSS_ANON_BOX(pageSequence, ":-moz-page-sequence")
 CSS_ANON_BOX(scrolledContent, ":-moz-scrolled-content")
+CSS_ANON_BOX(scrolledCanvas, ":-moz-scrolled-canvas")
+CSS_ANON_BOX(scrolledPageSequence, ":-moz-scrolled-page-sequence")
 CSS_ANON_BOX(columnContent, ":-moz-column-content")
 CSS_ANON_BOX(viewport, ":-moz-viewport")
 CSS_ANON_BOX(viewportScroll, ":-moz-viewport-scroll")

layout/style/ua.css

@@ -129,16 +129,8 @@
   display: block !important;
 }
 
-*|*::-moz-viewport, *|*::-moz-viewport-scroll, *|*::-moz-canvas {
-  display: block !important;
-  background-color: inherit;
-}
-
-*|*::-moz-viewport-scroll {
-  overflow: auto;
-}
-
-*|*::-moz-scrolled-content { 
+*|*::-moz-scrolled-content, *|*::-moz-scrolled-canvas,
+*|*::-moz-scrolled-page-sequence {
   /* e.g., text inputs, select boxes */
   padding: inherit;
   display: inherit;
@@ -155,6 +147,15 @@
   float: none !important;
 }
 
+*|*::-moz-viewport, *|*::-moz-viewport-scroll, *|*::-moz-canvas, *|*::-moz-scrolled-canvas {
+  display: block !important;
+  background-color: inherit;
+}
+
+*|*::-moz-viewport-scroll {
+  overflow: auto;
+}
+
 *|*::-moz-column-content { 
   /* the column boxes inside a column-flowed block */
   /* make unicode-bidi inherit, otherwise it has no effect on column boxes */
@@ -166,7 +167,7 @@
   height: 100%;
 }
 
-*|*::-moz-page, *|*::-moz-page-sequence {
+*|*::-moz-page, *|*::-moz-page-sequence, *|*::-moz-scrolled-page-sequence {
   display: block !important;
   background: transparent;
 }
@@ -199,7 +200,8 @@
     cursor: default !important;
   }
 
-  *|*::-moz-viewport, *|*::-moz-viewport-scroll, *|*::-moz-canvas {
+  *|*::-moz-viewport, *|*::-moz-viewport-scroll, *|*::-moz-canvas,
+  *|*::-moz-scrolled-canvas {
     background-color: #737373 !important;
   }