From 7792c4a45ffad9ec77ec363e97dda576f66d3747 Mon Sep 17 00:00:00 2001
From: Jonathan Watt <jwatt@jwatt.org>
Date: Sat, 24 May 2014 21:37:48 +0100
Subject: [PATCH] Bug 1011806 - Stop loading user-agent and user style sheets
 for SVG-as-an-image (the main UA sheets svg.css, html.css, etc. will still
 load on demand). r=bz CLOSED TREE

---
 content/svg/document/src/SVGDocument.cpp | 62 ++++++++++++++++++++++++
 layout/base/nsDocumentViewer.cpp         | 17 ++++++-
 layout/base/nsStyleSheetService.cpp      |  3 ++
 3 files changed, 81 insertions(+), 1 deletion(-)

diff --git a/content/svg/document/src/SVGDocument.cpp b/content/svg/document/src/SVGDocument.cpp
index 1c4820c1eec8..c5280aef7958 100644
--- a/content/svg/document/src/SVGDocument.cpp
+++ b/content/svg/document/src/SVGDocument.cpp
@@ -4,7 +4,15 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/dom/SVGDocument.h"
+
+#include "mozilla/css/Loader.h"
+#include "nsICategoryManager.h"
+#include "nsISimpleEnumerator.h"
+#include "nsIStyleSheetService.h"
+#include "nsISupportsPrimitives.h"
 #include "nsLayoutStylesheetCache.h"
+#include "nsNetUtil.h"
+#include "nsServiceManagerUtils.h"
 #include "nsString.h"
 #include "nsLiteralString.h"
 #include "nsIDOMSVGElement.h"
@@ -12,6 +20,7 @@
 #include "nsSVGElement.h"
 #include "mozilla/dom/SVGDocumentBinding.h"
 
+using namespace mozilla::css;
 using namespace mozilla::dom;
 
 namespace mozilla {
@@ -78,6 +87,59 @@ SVGDocument::EnsureNonSVGUserAgentStyleSheetsLoaded()
 
   mHasLoadedNonSVGUserAgentStyleSheets = true;
 
+  if (IsBeingUsedAsImage()) {
+    // nsDocumentViewer::CreateStyleSet skipped loading all user-agent/user
+    // style sheets in this case, but we'll need B2G/Fennec/Metro's
+    // content.css. We could load all the sheets registered with the
+    // nsIStyleSheetService (and maybe we should) but most likely it isn't
+    // desirable or necessary for foreignObject in SVG-as-an-image. Instead we
+    // only load the "agent-style-sheets" that nsStyleSheetService::Init()
+    // pulls in from the category manager. That keeps memory use of
+    // SVG-as-an-image down.
+    //
+    // We do this before adding UASheet() etc. below because
+    // EnsureOnDemandBuiltInUASheet prepends, and B2G/Fennec/Metro's
+    // content.css must come after UASheet() etc.
+    nsCOMPtr<nsICategoryManager> catMan =
+    do_GetService(NS_CATEGORYMANAGER_CONTRACTID);
+    if (catMan) {
+      nsCOMPtr<nsISimpleEnumerator> sheets;
+      catMan->EnumerateCategory("agent-style-sheets", getter_AddRefs(sheets));
+      if (sheets) {
+        bool hasMore;
+        while (NS_SUCCEEDED(sheets->HasMoreElements(&hasMore)) && hasMore) {
+          nsCOMPtr<nsISupports> sheet;
+          if (NS_FAILED(sheets->GetNext(getter_AddRefs(sheet))))
+            break;
+
+          nsCOMPtr<nsISupportsCString> icStr = do_QueryInterface(sheet);
+          MOZ_ASSERT(icStr,
+                     "category manager entries must be nsISupportsCStrings");
+
+          nsAutoCString name;
+          icStr->GetData(name);
+
+          nsXPIDLCString spec;
+          catMan->GetCategoryEntry("agent-style-sheets", name.get(),
+                                   getter_Copies(spec));
+
+          mozilla::css::Loader* cssLoader = CSSLoader();
+          if (cssLoader->GetEnabled()) {
+            nsCOMPtr<nsIURI> uri;
+            NS_NewURI(getter_AddRefs(uri), spec);
+            if (uri) {
+              nsRefPtr<nsCSSStyleSheet> cssSheet;
+              cssLoader->LoadSheetSync(uri, true, true, getter_AddRefs(cssSheet));
+              if (cssSheet) {
+                EnsureOnDemandBuiltInUASheet(cssSheet);
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+
   EnsureOnDemandBuiltInUASheet(nsLayoutStylesheetCache::NumberControlSheet());
   EnsureOnDemandBuiltInUASheet(nsLayoutStylesheetCache::FormsSheet());
   EnsureOnDemandBuiltInUASheet(nsLayoutStylesheetCache::HTMLSheet());
diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index 7bfe52358092..8bf47a442488 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -2188,7 +2188,22 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument,
   styleSet->BeginUpdate();
   
   // The document will fill in the document sheets when we create the presshell
-  
+
+  if (aDocument->IsBeingUsedAsImage()) {
+    MOZ_ASSERT(aDocument->IsSVG(),
+               "Do we want to skip most sheets for this new image type?");
+
+    // SVG-as-an-image must be kept as light and small as possible. We
+    // deliberately skip loading everything and leave svg.css (and html.css and
+    // xul.css) to be loaded on-demand.
+    // XXXjwatt Nothing else is loaded on-demand, but I don't think that
+    // should matter for SVG-as-an-image. If it does, I want to know why!
+
+    // Caller will handle calling EndUpdate, per contract.
+    *aStyleSet = styleSet;
+    return NS_OK;
+  }
+
   // Handle the user sheets.
   nsCSSStyleSheet* sheet = nullptr;
   if (nsContentUtils::IsInChromeDocshell(aDocument)) {
diff --git a/layout/base/nsStyleSheetService.cpp b/layout/base/nsStyleSheetService.cpp
index 85f5f815ff6c..aabec1a844bb 100644
--- a/layout/base/nsStyleSheetService.cpp
+++ b/layout/base/nsStyleSheetService.cpp
@@ -97,6 +97,9 @@ nsStyleSheetService::FindSheetByURI(const nsCOMArray<nsIStyleSheet> &sheets,
 nsresult
 nsStyleSheetService::Init()
 {
+  // If you make changes here, consider whether
+  // SVGDocument::EnsureNonSVGUserAgentStyleSheetsLoaded should be updated too.
+
   // Child processes get their style sheets from the ContentParent.
   if (XRE_GetProcessType() == GeckoProcessType_Content) {
     return NS_OK;