Don't trigger re-layout when stroke-dash{array,offset} changes

Since we no longer include the dash-effect when computing
(appromixating) the stroke bounds, we don't need to trigger (re)layout
when they change.

This can help eliminate layouts for example for "line animations" like
the one on https://jakearchibald.com/2013/animated-line-drawing-svg/

Bug: 435097
Change-Id: Iaf5298620889b6ed0cb10437514bb8af3104cc35
Reviewed-on: https://chromium-review.googlesource.com/c/1489202Reviewed-by: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#635931}

third_party/blink/renderer/core/style/svg_computed_style.cc

@@ -167,16 +167,19 @@ bool SVGComputedStyle::DiffNeedsLayoutAndPaintInvalidation(
       other->svg_noninherited_flags.f.vector_effect)
     return true;
 
-  // Some stroke properties, requires relayouts, as the cached stroke boundaries
+  // Some stroke properties require relayouts as the cached stroke boundaries
   // need to be recalculated.
   if (stroke.Get() != other->stroke.Get()) {
     if (stroke->width != other->stroke->width ||
         stroke->paint != other->stroke->paint ||
         stroke->miter_limit != other->stroke->miter_limit ||
-        *stroke->dash_array != *other->stroke->dash_array ||
-        stroke->dash_offset != other->stroke->dash_offset ||
         stroke->visited_link_paint != other->stroke->visited_link_paint)
       return true;
+    // If the dash array is toggled from/to 'none' we need to relayout, because
+    // some shapes will decide on which codepath to use based on the presence
+    // of a dash array.
+    if (stroke->dash_array->IsEmpty() != other->stroke->dash_array->IsEmpty())
+      return true;
   }
 
   // The geometry properties require a re-layout.
@@ -188,8 +191,16 @@ bool SVGComputedStyle::DiffNeedsLayoutAndPaintInvalidation(
 
 bool SVGComputedStyle::DiffNeedsPaintInvalidation(
     const SVGComputedStyle* other) const {
-  if (stroke->opacity != other->stroke->opacity)
-    return true;
+  if (stroke.Get() != other->stroke.Get()) {
+    if (stroke->opacity != other->stroke->opacity)
+      return true;
+    // Changes to the dash effect only require a repaint because we don't
+    // include it when computing (approximating) the stroke boundaries during
+    // layout.
+    if (stroke->dash_offset != other->stroke->dash_offset ||
+        *stroke->dash_array != *other->stroke->dash_array)
+      return true;
+  }
 
   // Painting related properties only need paint invalidation.
   if (misc.Get() != other->misc.Get()) {