Fix invalid selection produced when dragging mouse outside the SVG text element

third_party/WebKit/Source/core/layout/svg/SVGLayoutSupport.cpp

Index: third_party/WebKit/Source/core/layout/svg/SVGLayoutSupport.cpp
diff --git a/third_party/WebKit/Source/core/layout/svg/SVGLayoutSupport.cpp b/third_party/WebKit/Source/core/layout/svg/SVGLayoutSupport.cpp
index 32073042bd914cd8999f8fd2c593feade0f70a23..7e9b0cbaca3a30dfaa7b4aa46e364de01fca71c1 100644
--- a/third_party/WebKit/Source/core/layout/svg/SVGLayoutSupport.cpp
+++ b/third_party/WebKit/Source/core/layout/svg/SVGLayoutSupport.cpp
@@ -44,6 +44,17 @@
 
 namespace blink {
 
+struct SearchCandidate {
+    SearchCandidate() {}
+    SearchCandidate(LayoutObject* layoutObject, float dist)
+        : candidateLayoutObject(layoutObject)
+        , distance(dist)
+    {
+    }
+    LayoutObject* candidateLayoutObject;
+    float distance;
+};
+
 static inline LayoutRect adjustedEnclosingIntRect(const FloatRect& rect,
     const AffineTransform& rootTransform, float strokeWidthForHairlinePadding)
 {
@@ -476,4 +487,64 @@ float SVGLayoutSupport::calculateScreenFontSizeScalingFactor(const LayoutObject*
     return narrowPrecisionToFloat(sqrt((pow(ctm.xScale(), 2) + pow(ctm.yScale(), 2)) / 2));
 }
 
+static inline bool compareCandidateDistance(const SearchCandidate& r1, const SearchCandidate& r2)
+{
+    return r1.distance < r2.distance;
+}
+
+static inline float distanceToChildLayoutObject(LayoutObject* child, const FloatPoint& point)
+{
+    const AffineTransform& localToParentTransform = child->localToParentTransform();
+    if (!localToParentTransform.isInvertible())
+        return std::numeric_limits<float>::max();
+    FloatPoint childLocalPoint = localToParentTransform.inverse().mapPoint(point);
+    return child->objectBoundingBox().squaredDistanceTo(childLocalPoint);
+}
+
+LayoutObject* SVGLayoutSupport::findClosestLayoutSVGText(LayoutObject* layoutObject, const FloatPoint& point)
+{
+    // Try to find the closest LayoutSVGText. If not find this level, try to search on candidates.
+    LayoutObject* closestLayoutObject = nullptr;
+    float closestDistance = std::numeric_limits<float>::max();
+    Vector<SearchCandidate> candidates;
+    for (LayoutObject* child = layoutObject->slowLastChild(); child; child = child->previousSibling()) {
+        if (child->isSVGText()) {
+            float distance = distanceToChildLayoutObject(child, point);
+            if (distance >= closestDistance)
+                continue;
+            candidates.clear();
+            closestLayoutObject = child;
+            closestDistance = distance;
+            continue;
+        }
+
+        if (child->isSVGContainer() && !layoutObject->isSVGHiddenContainer()) {
+            float distance = distanceToChildLayoutObject(child, point);
+            if (distance > closestDistance)
+                continue;
+            candidates.append(SearchCandidate(child, distance));
+        }
+    }
+
+    if (closestLayoutObject && closestLayoutObject->isSVGText())
+        return closestLayoutObject;
+
+    if (candidates.isEmpty())
+        return nullptr;
+
+    // Sort using the distance between the mouse point and a candidate.
+    // Because if the distance is close, It is high priority to search LayoutSVGText.
+    std::stable_sort(candidates.begin(), candidates.end(), compareCandidateDistance);
+
+    // If not find LayoutSVGText on this level of tree, try to search it on sub-tree of |condidate|.
+    for (SearchCandidate& searchCandidate : candidates) {
+        LayoutObject* candidateLayoutObject = searchCandidate.candidateLayoutObject;
+        FloatPoint candidateLocalPoint = candidateLayoutObject->localToParentTransform().inverse().mapPoint(point);
+        if (LayoutObject* result = findClosestLayoutSVGText(candidateLayoutObject, candidateLocalPoint))
+            return result;
+    }
+
+    return nullptr;
+}
+
 }