Reland "Remove gpu buffer reads from default path renderer."

This reverts commit 30b355a49e120d7aef70ce454b6bd4c58ff97ce6.

Reason for revert: relanding with fix

Original change's description:
> Revert "Remove gpu buffer reads from default path renderer."
>
> This reverts commit 64241b8edb4dddaec62b78f3d722c7e56364d869.
>
> Reason for revert: hitting new assert on starting point
>
> Original change's description:
> > Remove gpu buffer reads from default path renderer.
> >
> > I don't actually expect to see much perf gain from this one because the
> > reads happen when we've run out of space in our vertex buffer and need
> > a new allocation. So they happen pretty rarely.
> >
> > Change-Id: Iabe2e7cebf363659180409075a1a7fc6c03d0a22
> > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/364618
> > Commit-Queue: Greg Daniel <egdaniel@google.com>
> > Reviewed-by: Chris Dalton <csmartdalton@google.com>
>
> TBR=egdaniel@google.com,csmartdalton@google.com
>
> Change-Id: I4c160ee692222f7c64cc63db2044fdc958eae551
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/365482
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Greg Daniel <egdaniel@google.com>

TBR=egdaniel@google.com,csmartdalton@google.com

# Not skipping CQ checks because this is a reland.

Change-Id: I97d613ca9adef0d425cc5ab22923d95297ca0afe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/365486
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
diff --git a/src/gpu/ops/GrDefaultPathRenderer.cpp b/src/gpu/ops/GrDefaultPathRenderer.cpp
index 938fbbe..6f4be70 100644
--- a/src/gpu/ops/GrDefaultPathRenderer.cpp
+++ b/src/gpu/ops/GrDefaultPathRenderer.cpp
@@ -87,25 +87,29 @@
      *  Path verbs
      */
     void moveTo(const SkPoint& p) {
-        needSpace(1);
+        this->needSpace(1);
 
-        fSubpathIndexStart = this->currentIndex();
-        *(fCurVert++) = p;
-    }
-
-    void addLine(const SkPoint& p) {
-        needSpace(1, this->indexScale());
-
-        if (this->isIndexed()) {
-            uint16_t prevIdx = this->currentIndex() - 1;
-            appendCountourEdgeIndices(prevIdx);
+        if (!this->isHairline()) {
+            fSubpathIndexStart = this->currentIndex();
+            fSubpathStartPoint = p;
         }
         *(fCurVert++) = p;
     }
 
+    void addLine(const SkPoint pts[]) {
+        this->needSpace(1, this->indexScale(), &pts[0]);
+
+        if (this->isIndexed()) {
+            uint16_t prevIdx = this->currentIndex() - 1;
+            this->appendCountourEdgeIndices(prevIdx);
+        }
+        *(fCurVert++) = pts[1];
+    }
+
     void addQuad(const SkPoint pts[], SkScalar srcSpaceTolSqd, SkScalar srcSpaceTol) {
         this->needSpace(GrPathUtils::kMaxPointsPerCurve,
-                        GrPathUtils::kMaxPointsPerCurve * this->indexScale());
+                        GrPathUtils::kMaxPointsPerCurve * this->indexScale(),
+                        &pts[0]);
 
         // First pt of quad is the pt we ended on in previous step
         uint16_t firstQPtIdx = this->currentIndex() - 1;
@@ -114,7 +118,7 @@
                 GrPathUtils::quadraticPointCount(pts, srcSpaceTol));
         if (this->isIndexed()) {
             for (uint16_t i = 0; i < numPts; ++i) {
-                appendCountourEdgeIndices(firstQPtIdx + i);
+                this->appendCountourEdgeIndices(firstQPtIdx + i);
             }
         }
     }
@@ -130,7 +134,8 @@
 
     void addCubic(const SkPoint pts[], SkScalar srcSpaceTolSqd, SkScalar srcSpaceTol) {
         this->needSpace(GrPathUtils::kMaxPointsPerCurve,
-                        GrPathUtils::kMaxPointsPerCurve * this->indexScale());
+                        GrPathUtils::kMaxPointsPerCurve * this->indexScale(),
+                        &pts[0]);
 
         // First pt of cubic is the pt we ended on in previous step
         uint16_t firstCPtIdx = this->currentIndex() - 1;
@@ -139,7 +144,7 @@
                 GrPathUtils::cubicPointCount(pts, srcSpaceTol));
         if (this->isIndexed()) {
             for (uint16_t i = 0; i < numPts; ++i) {
-                appendCountourEdgeIndices(firstCPtIdx + i);
+                this->appendCountourEdgeIndices(firstCPtIdx + i);
             }
         }
     }
@@ -158,7 +163,7 @@
                     this->moveTo(pts[0]);
                     break;
                 case SkPath::kLine_Verb:
-                    this->addLine(pts[1]);
+                    this->addLine(pts);
                     break;
                 case SkPath::kConic_Verb:
                     this->addConic(iter.conicWeight(), pts, srcSpaceTolSqd, srcSpaceTol);
@@ -289,17 +294,25 @@
         }
     }
 
-    void needSpace(int vertsNeeded, int indicesNeeded = 0) {
+    void needSpace(int vertsNeeded, int indicesNeeded = 0, const SkPoint* lastPoint = nullptr) {
         if (fCurVert + vertsNeeded > fVertices + fVerticesInChunk ||
             fCurIdx + indicesNeeded > fIndices + fIndicesInChunk) {
             // We are about to run out of space (possibly)
 
+#ifdef SK_DEBUG
             // To maintain continuity, we need to remember one or two points from the current mesh.
             // Lines only need the last point, fills need the first point from the current contour.
             // We always grab both here, and append the ones we need at the end of this process.
-            SkPoint lastPt = *(fCurVert - 1);
             SkASSERT(fSubpathIndexStart < fVerticesInChunk);
-            SkPoint subpathStartPt = fVertices[fSubpathIndexStart];
+            // This assert is reading from the gpu buffer fVertices and will be slow, but for debug
+            // that is okay.
+            if (!this->isHairline()) {
+                SkASSERT(fSubpathStartPoint == fVertices[fSubpathIndexStart]);
+            }
+            if (lastPoint) {
+                SkASSERT(*(fCurVert - 1) == *lastPoint);
+            }
+#endif
 
             // Draw the mesh we've accumulated, and put back any unused space
             this->createMeshAndPutBackReserve();
@@ -307,11 +320,15 @@
             // Get new buffers
             this->allocNewBuffers();
 
-            // Append copies of the points we saved so the two meshes will weld properly
-            if (!this->isHairline()) {
-                *(fCurVert++) = subpathStartPt;
+            // On moves we don't need to copy over any points to the new buffer and we pass in a
+            // null lastPoint.
+            if (lastPoint) {
+                // Append copies of the points we saved so the two meshes will weld properly
+                if (!this->isHairline()) {
+                    *(fCurVert++) = fSubpathStartPoint;
+                }
+                *(fCurVert++) = *lastPoint;
             }
-            *(fCurVert++) = lastPt;
         }
     }
 
@@ -331,6 +348,7 @@
     uint16_t* fIndices;
     uint16_t* fCurIdx;
     uint16_t fSubpathIndexStart;
+    SkPoint fSubpathStartPoint;
 
     SkTDArray<GrSimpleMesh*>* fMeshes;
 };