[LayoutNG] Enable LayoutNGPaintFragments in virtual/layout_ng

This patch enables LayoutNGPaintFragments in virtual/layout_ng,
and also merges layout_ng and layout_ng_paint.

There are additional failures; some are just to be rebaselined.
I will analyze and cleanup in following patches.

Bug: 792329, 714962
Change-Id: Ie61d9672e3d4f44847ef8771214c16e993245943
Reviewed-on: https://chromium-review.googlesource.com/804803Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522469}

third_party/WebKit/LayoutTests/FlagExpectations/enable-blink-features=LayoutNG

@@ -8060,7 +8060,6 @@ crbug.com/591099 virtual/layout_ng/fast/block/float/shrink-to-avoid-float-comple
 crbug.com/591099 virtual/layout_ng/fast/block/margin-collapse/self-collapsing-cols-creates-block-formatting-context.html [ Pass ]
 crbug.com/591099 virtual/layout_ng/overflow/overflow-basic-003.html [ Pass ]
 crbug.com/591099 virtual/layout_ng/overflow/overflow-bug-chrome-ng-001.html [ Pass ]
-crbug.com/591099 virtual/layout_ng_paint/ [ Skip ]
 crbug.com/591099 virtual/mojo-blobs/ [ Skip ]
 crbug.com/591099 virtual/mojo-localstorage/ [ Skip ]
 crbug.com/591099 virtual/mouseevent_fractional/fast/events/anchor-empty-focus.html [ Failure ]

third_party/WebKit/LayoutTests/VirtualTestSuites

@@ -370,62 +370,74 @@
   {
     "prefix": "layout_ng",
     "base": "fast/block/basic",
-    "args": ["--enable-blink-features=LayoutNG"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
     "prefix": "layout_ng",
     "base": "fast/block/margin-collapse",
-    "args": ["--enable-blink-features=LayoutNG"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
     "prefix": "layout_ng",
     "base": "fast/block/float",
-    "args": ["--enable-blink-features=LayoutNG"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
     "prefix": "layout_ng",
     "base": "external/wpt/css/CSS2/linebox",
-    "args": ["--enable-blink-features=LayoutNG"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
     "prefix": "layout_ng",
     "base": "external/wpt/css/CSS2/normal-flow",
-    "args": ["--enable-blink-features=LayoutNG"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
     "prefix": "layout_ng",
     "base": "external/wpt/css/CSS2/abspos",
-    "args": ["--enable-blink-features=LayoutNG"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
     "prefix": "layout_ng",
     "base": "external/wpt/css/CSS2/positioning",
-    "args": ["--enable-blink-features=LayoutNG"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
     "prefix": "layout_ng",
     "base": "external/wpt/css/CSS2/floats",
-    "args": ["--enable-blink-features=LayoutNG"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
     "prefix": "layout_ng",
     "base": "external/wpt/css/CSS2/floats-clear",
-    "args": ["--enable-blink-features=LayoutNG"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
     "prefix": "layout_ng",
     "base": "overflow",
-    "args": ["--enable-blink-features=LayoutNG"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
-    "prefix": "layout_ng_paint",
+    "prefix": "layout_ng",
     "base": "fast/inline",
-    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
-    "prefix": "layout_ng_paint",
+    "prefix": "layout_ng",
     "base": "fast/writing-mode",
-    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments"]
+    "args": ["--enable-blink-features=LayoutNG,LayoutNGPaintFragments",
+             "--enable-slimming-paint-v175"]
   },
   {
     "prefix": "feature-policy",