From ab415510c2e8b0c8fbe70ea9b591c61bdbe0f7f9 Mon Sep 17 00:00:00 2001
From: Bobby Holley <bobbyholley@gmail.com>
Date: Wed, 26 Jul 2017 16:57:13 -0700
Subject: [PATCH] Bug 1384769 - Break TraversalFlags::ForReconstruct down into
 several independent pieces. r=emilio

These will be useful in followup work.

MozReview-Commit-ID: Dyp9R0PG36v
---
 layout/style/ServoStyleSet.cpp |  8 ++++++--
 layout/style/ServoTypes.h      | 16 ++++++++++++----
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/layout/style/ServoStyleSet.cpp b/layout/style/ServoStyleSet.cpp
index fc21cc1ea517..2d3d26af6d27 100644
--- a/layout/style/ServoStyleSet.cpp
+++ b/layout/style/ServoStyleSet.cpp
@@ -288,7 +288,7 @@ ServoStyleSet::PrepareAndTraverseSubtree(
   const SnapshotTable& snapshots = Snapshots();
 
   bool isInitial = !aRoot->HasServoData();
-  bool forReconstruct = !!(aFlags & ServoTraversalFlags::ForReconstruct);
+  bool forReconstruct = !!(aFlags & ServoTraversalFlags::AggressivelyForgetful);
   bool postTraversalRequired =
     Servo_TraverseSubtree(aRoot, mRawSet.get(), &snapshots, aFlags);
   MOZ_ASSERT(!(isInitial || forReconstruct) || !postTraversalRequired);
@@ -839,8 +839,12 @@ ServoStyleSet::StyleSubtreeForReconstruct(Element* aRoot)
 {
   PreTraverse(aRoot);
 
+  auto flags = ServoTraversalFlags::Forgetful |
+               ServoTraversalFlags::AggressivelyForgetful |
+               ServoTraversalFlags::ClearDirtyDescendants |
+               ServoTraversalFlags::ClearAnimationOnlyDirtyDescendants;
   DebugOnly<bool> postTraversalRequired =
-    PrepareAndTraverseSubtree(aRoot, ServoTraversalFlags::ForReconstruct);
+    PrepareAndTraverseSubtree(aRoot, flags);
   MOZ_ASSERT(!postTraversalRequired);
 }
 
diff --git a/layout/style/ServoTypes.h b/layout/style/ServoTypes.h
index 8c68f64f9d87..f0d57eb5d741 100644
--- a/layout/style/ServoTypes.h
+++ b/layout/style/ServoTypes.h
@@ -58,10 +58,18 @@ enum class ServoTraversalFlags : uint32_t {
   ForCSSRuleChanges = 1 << 1,
   // Traverse only unstyled children of the root (and their descendants).
   UnstyledChildrenOnly = 1 << 2,
-  // Traverses in a mode that doesn't generate any change hints, which is what's
-  // required when handling frame reconstruction.  The change hints in this case
-  // are unneeded, since the old frames have already been destroyed.
-  ForReconstruct = 1 << 3,
+  // A forgetful traversal ignores the previous state of the frame tree, and
+  // thus does not compute damage or maintain other state describing the styles
+  // pre-traversal. A forgetful traversal is usually the right thing if you
+  // aren't going to do a post-traversal.
+  Forgetful = 1 << 3,
+  // Actively seeks out and clears change hints that may have been posted into
+  // the tree. Nonsensical without also passing Forgetful.
+  AggressivelyForgetful = 1 << 4,
+  // Clears the dirty descendants bit in the subtree.
+  ClearDirtyDescendants = 1 << 5,
+  // Clears the animation-only dirty descendants bit in the subtree.
+  ClearAnimationOnlyDirtyDescendants = 1 << 6,
 };
 
 MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(ServoTraversalFlags)