Replace SkTSwap with std::swap/swap.

Skia is moving to normalize on std::swap instead of its own SkTSwap.
This removes the use of SkTSwap from PDFium so that Skia can remove it.

Change-Id: If77708c1f363f4fd82a4c7905c7fbb2060900532
Reviewed-on: https://pdfium-review.googlesource.com/35470
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
diff --git a/core/fxge/skia/fx_skia_device.cpp b/core/fxge/skia/fx_skia_device.cpp
index 0329eac..adc02fe 100644
--- a/core/fxge/skia/fx_skia_device.cpp
+++ b/core/fxge/skia/fx_skia_device.cpp
@@ -2052,8 +2052,8 @@
       // if the gradient is horizontal or vertical, modify the draw rectangle
       if (pts[0].fX == pts[1].fX) {  // vertical
         if (pts[0].fY > pts[1].fY) {
-          SkTSwap(pts[0].fY, pts[1].fY);
-          SkTSwap(clipStart, clipEnd);
+          std::swap(pts[0].fY, pts[1].fY);
+          std::swap(clipStart, clipEnd);
         }
         if (clipStart)
           skRect.fTop = SkTMax(skRect.fTop, pts[0].fY);
@@ -2061,8 +2061,8 @@
           skRect.fBottom = SkTMin(skRect.fBottom, pts[1].fY);
       } else if (pts[0].fY == pts[1].fY) {  // horizontal
         if (pts[0].fX > pts[1].fX) {
-          SkTSwap(pts[0].fX, pts[1].fX);
-          SkTSwap(clipStart, clipEnd);
+          std::swap(pts[0].fX, pts[1].fX);
+          std::swap(clipStart, clipEnd);
         }
         if (clipStart)
           skRect.fLeft = SkTMax(skRect.fLeft, pts[0].fX);