[FCP++] Rename PaintTracking flag to FCPPlusPlus

Rename PaintTracking flag to FirstContentfulPaintPlusPlus. The flag is meant to
serve specifically to FCP++ metrics. So the naming should reflect this goal.

This CL renames the PaintTracking flag in runtime_enabled_features.

Bug: 869924
Change-Id: Ib3cbd8ac21ab962e87626edf74e13dfc8fde486e
Reviewed-on: https://chromium-review.googlesource.com/c/1338237
Commit-Queue: Liquan (Max) Gǔ <maxlg@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608524}

third_party/blink/renderer/core/layout/layout_object.cc

@@ -3262,7 +3262,7 @@ void LayoutObject::WillBeRemovedFromTree() {
     FindReferencingScrollAnchors(this, kClear);
   }
 
-  if (RuntimeEnabledFeatures::PaintTrackingEnabled()) {
+  if (RuntimeEnabledFeatures::FirstContentfulPaintPlusPlusEnabled()) {
     if (LocalFrameView* frame_view = GetFrameView()) {
       frame_view->GetPaintTracker().NotifyNodeRemoved(*this);
     }

third_party/blink/renderer/core/paint/image_paint_timing_detector_test.cc

@@ -21,13 +21,15 @@
 
 namespace blink {
 
-class ImagePaintTimingDetectorTest : public PageTestBase,
-                                     private ScopedPaintTrackingForTest {
+class ImagePaintTimingDetectorTest
+    : public PageTestBase,
+      private ScopedFirstContentfulPaintPlusPlusForTest {
   using CallbackQueue = std::queue<WebLayerTreeView::ReportTimeCallback>;
 
  public:
   ImagePaintTimingDetectorTest()
-      : ScopedPaintTrackingForTest(true), base_url_("http://www.test.com/"){};
+      : ScopedFirstContentfulPaintPlusPlusForTest(true),
+        base_url_("http://www.test.com/"){};
 
   ~ImagePaintTimingDetectorTest() override {
     Platform::Current()

third_party/blink/renderer/core/paint/pre_paint_tree_walk.cc

@@ -133,7 +133,7 @@ void PrePaintTreeWalk::Walk(LocalFrameView& frame_view) {
 
   if (RuntimeEnabledFeatures::JankTrackingEnabled())
     frame_view.GetJankTracker().NotifyPrePaintFinished();
-  if (RuntimeEnabledFeatures::PaintTrackingEnabled())
+  if (RuntimeEnabledFeatures::FirstContentfulPaintPlusPlusEnabled())
     frame_view.GetPaintTracker().NotifyPrePaintFinished();
 
   context_storage_.pop_back();
@@ -375,7 +375,7 @@ void PrePaintTreeWalk::WalkInternal(const LayoutObject& object,
         object, paint_invalidator_context.old_visual_rect,
         *paint_invalidator_context.painting_layer);
   }
-  if (RuntimeEnabledFeatures::PaintTrackingEnabled()) {
+  if (RuntimeEnabledFeatures::FirstContentfulPaintPlusPlusEnabled()) {
     object.GetFrameView()->GetPaintTracker().NotifyObjectPrePaint(
         object, *paint_invalidator_context.painting_layer);
   }

third_party/blink/renderer/core/paint/text_paint_timing_detector_test.cc

@@ -6,15 +6,17 @@
 #include "third_party/blink/renderer/core/paint/paint_tracker.h"
 #include "third_party/blink/renderer/core/testing/core_unit_test_helper.h"
 #include "third_party/blink/renderer/platform/runtime_enabled_features.h"
+#include "third_party/blink/renderer/platform/testing/runtime_enabled_features_test_helpers.h"
 
 namespace blink {
 
-class TextPaintTimingDetectorTest : public RenderingTest {
+class TextPaintTimingDetectorTest
+    : public RenderingTest,
+      private ScopedFirstContentfulPaintPlusPlusForTest {
  public:
-  void SetUp() override {
-    RenderingTest::SetUp();
-    RuntimeEnabledFeatures::SetPaintTrackingEnabled(true);
-  }
+  TextPaintTimingDetectorTest()
+      : ScopedFirstContentfulPaintPlusPlusForTest(true) {}
+  void SetUp() override { RenderingTest::SetUp(); }
 
  protected:
   LocalFrameView& GetFrameView() { return *GetFrame().View(); }

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -488,6 +488,12 @@
       name: "FileSystem",
       status: "stable",
     },
+    // FirstContentfulPaintPlusPlus enables the Largest Text Paint metric, Last
+    // Text Paint metric, Largest Image Paint metric and Last Image Paint
+    // metric. See also: http://bit.ly/fcp_plus_plus
+    {
+      name: "FirstContentfulPaintPlusPlus",
+    },
     {
       name: "FontCacheScaling",
       status: "test",
@@ -906,12 +912,6 @@
       name: "PaintTouchActionRects",
       status: "stable",
     },
-    // PaintTracking enables the Largest Text Paint metric, Last Text Paint
-    // metric, Largest Image Paint metric and Last Image Paint metric.
-    // See also: https://docs.google.com/document/d/1DRVd4a2VU8-yyWftgOparZF-sf16daf0vfbsHuz2rws/edit
-    {
-      name: "PaintTracking",
-    },
     {
       name: "PaintUnderInvalidationChecking",
       settable_from_internals: true,