Bug 1354772 - Part 2. Compute URLValueData::mMightHaveRef when need. r=heycam

MozReview-Commit-ID: 8t5tKrjB1cz

--HG--
extra : rebase_source : cda9e15dcb51aeedf6bb532dd702247e60e59304

layout/style/nsCSSValue.cpp

@@ -45,6 +45,19 @@ IsLocalRefURL(nsStringBuffer* aString)
   return false;
 }
 
+static bool
+MightHaveRef(nsStringBuffer* aString)
+{
+  char16_t* current = static_cast<char16_t*>(aString->Data());
+  for (; *current != '\0'; current++) {
+    if (*current == '#') {
+      return true;
+    }
+  }
+
+  return false;
+}
+
 nsCSSValue::nsCSSValue(int32_t aValue, nsCSSUnit aUnit)
   : mUnit(aUnit)
 {
@@ -2895,6 +2908,18 @@ css::URLValueData::HasRef() const
   return false;
 }
 
+bool
+css::URLValueData::MightHaveRef() const
+{
+  if (mMightHaveRef.isNothing()) {
+    // ::MightHaveRef is O(N), use it only use it only when MightHaveRef is
+    // called.
+    mMightHaveRef.emplace(::MightHaveRef(mString));
+  }
+
+  return mMightHaveRef.value();
+}
+
 already_AddRefed<nsIURI>
 css::URLValueData::ResolveLocalRef(nsIURI* aURI) const
 {

layout/style/nsCSSValue.h

@@ -135,6 +135,14 @@ public:
 
   bool HasRef() const;
 
+  // This function takes a guess whether the URL has a fragment, by searching
+  // for a hash character. It definitely returns false if we know it can't
+  // have a fragment because it has no hash character.
+  //
+  // MightHaveRef can be used in any thread, whereas HasRef can only be used
+  // in the main thread.
+  bool MightHaveRef() const;
+
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(URLValueData)
 
   // When matching a url with mIsLocalRef set, resolve it against aURI;
@@ -159,6 +167,7 @@ private:
   mutable bool mURIResolved;
   // mIsLocalRef is set when url starts with a U+0023 number sign(#) character.
   mutable Maybe<bool> mIsLocalRef;
+  mutable Maybe<bool> mMightHaveRef;
 
 protected:
   virtual ~URLValueData() = default;

layout/style/nsStyleStruct.cpp

@@ -3028,11 +3028,11 @@ nsStyleImageLayers::Layer::CalcDifference(const nsStyleImageLayers::Layer& aNewL
     // not, it "must" not link to a SVG mask.
     bool maybeSVGMask = false;
     if (mImage.GetURLValue()) {
-      maybeSVGMask = mImage.GetURLValue()->HasRef();
+      maybeSVGMask = mImage.GetURLValue()->MightHaveRef();
     }
 
     if (!maybeSVGMask && aNewLayer.mImage.GetURLValue()) {
-      maybeSVGMask = aNewLayer.mImage.GetURLValue()->HasRef();
+      maybeSVGMask = aNewLayer.mImage.GetURLValue()->MightHaveRef();
     }
 
     // Return nsChangeHint_UpdateOverflow if either URI might link to an SVG