Revert "GrTessellator: handle three consecutive collinear edges."

This reverts commit 26bb0e66f28c41cb1e8e39f00d848997fd33d97c.

Reason for revert: segfaulty

Here's a log with a stacktrace:

https://chromium-swarm.appspot.com/task?id=3e658f7aa40dbb10&refresh=10

Original change's description:
> GrTessellator: handle three consecutive collinear edges.
> 
> In some cases, splitting may produce three consecutive edges which
> are collinear. The first one was being merged out, causing the third
> one to be missed.
> 
> The fix is to switch the arguments to merge_edges_*, ensuring that the
> second parameter (the destination edge) is never merged out.
> 
> Bug: 851409.
> Change-Id: I70fbbc506e97a26b259c1443b6d1787adec0f9b0
> Reviewed-on: https://skia-review.googlesource.com/138561
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> Commit-Queue: Stephen White <senorblanco@chromium.org>

TBR=robertphillips@google.com,senorblanco@chromium.org

Change-Id: I6ecfb4c487d6f96e9fae7b8b40d74162354ed57c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 851409.
Reviewed-on: https://skia-review.googlesource.com/138640
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>

2 files changed, 5 insertions, 18 deletions

diff --git a/src/gpu/GrTessellator.cpp b/src/gpu/GrTessellator.cpp
index 649092001d..6cd54380e6 100644
--- a/src/gpu/GrTessellator.cpp
+++ b/src/gpu/GrTessellator.cpp
@@ -1055,16 +1055,16 @@ void merge_collinear_edges(Edge* edge, EdgeList* activeEdges, Vertex** current,
     for (;;) {
         if (edge->fPrevEdgeAbove && (edge->fTop == edge->fPrevEdgeAbove->fTop ||
                                      !edge->fPrevEdgeAbove->isLeftOf(edge->fTop))) {
-            merge_edges_above(edge->fPrevEdgeAbove, edge, activeEdges, current, c);
+            merge_edges_above(edge, edge->fPrevEdgeAbove, activeEdges, current, c);
         } else if (edge->fNextEdgeAbove && (edge->fTop == edge->fNextEdgeAbove->fTop ||
                                             !edge->isLeftOf(edge->fNextEdgeAbove->fTop))) {
-            merge_edges_above(edge->fNextEdgeAbove, edge, activeEdges, current, c);
+            merge_edges_above(edge, edge->fNextEdgeAbove, activeEdges, current, c);
         } else if (edge->fPrevEdgeBelow && (edge->fBottom == edge->fPrevEdgeBelow->fBottom ||
                                      !edge->fPrevEdgeBelow->isLeftOf(edge->fBottom))) {
-            merge_edges_below(edge->fPrevEdgeBelow, edge, activeEdges, current, c);
+            merge_edges_below(edge, edge->fPrevEdgeBelow, activeEdges, current, c);
         } else if (edge->fNextEdgeBelow && (edge->fBottom == edge->fNextEdgeBelow->fBottom ||
                                             !edge->isLeftOf(edge->fNextEdgeBelow->fBottom))) {
-            merge_edges_below(edge->fNextEdgeBelow, edge, activeEdges, current, c);
+            merge_edges_below(edge, edge->fNextEdgeBelow, activeEdges, current, c);
         } else {
             break;
         }
diff --git a/tests/TessellatingPathRendererTests.cpp b/tests/TessellatingPathRendererTests.cpp
index 0c7a5ca4c5..a9913769df 100644
--- a/tests/TessellatingPathRendererTests.cpp
+++ b/tests/TessellatingPathRendererTests.cpp
@@ -560,7 +560,7 @@ static SkPath create_path_38() {
     return path;
 }
 
-// Reduction from crbug.com/851409. Exercises collinear last vertex.
+// Reduction from crbug.com/851409.
 static SkPath create_path_39() {
     SkPath path;
     path.moveTo(2072553216, 0);
@@ -571,18 +571,6 @@ static SkPath create_path_39() {
     return path;
 }
 
-// Another reduction from crbug.com/851409. Exercises two sequential collinear edges.
-static SkPath create_path_40() {
-    SkPath path;
-    path.moveTo(2072553216, 0);
-    path.lineTo(2072553216, 1);
-    path.lineTo(2072553472, -13);
-    path.lineTo(2072553216, 0);
-    path.lineTo(2072553472, -6);
-    path.lineTo(2072553472, -13);
-    return path;
-}
-
 static std::unique_ptr<GrFragmentProcessor> create_linear_gradient_processor(GrContext* ctx) {
 
     SkPoint pts[2] = { {0, 0}, {1, 1} };
@@ -682,5 +670,4 @@ DEF_GPUTEST_FOR_ALL_CONTEXTS(TessellatingPathRendererTests, reporter, ctxInfo) {
     test_path(ctx, rtc.get(), create_path_37());
     test_path(ctx, rtc.get(), create_path_38(), SkMatrix(), GrAAType::kCoverage);
     test_path(ctx, rtc.get(), create_path_39());
-    test_path(ctx, rtc.get(), create_path_40());
 }