Remove no-op paint layer flag and compositing state query

First in a series of changes to get rid of the
DisableCompositingQueryAsserts in PaintLayerPainter::Paint.

kPaintLayerUncachedClipRects is only used to determine whether a paint
layer should create a subsequence (for potential benefits of caching/
reusing the subsequence). However, it is currently only set if
kGlobalPaintFlattenCompositingLayers is set (either manually in
data_transfer.cc or via the code in PaintLayerPainter::Paint).

If that global flag is set ShouldCreateSubsequence always returns false,
so the kPaintLayerUncachedClipRects flag is unnecessary. Removing this
code gets rid of 1 out of 3 compositing queries in this codepath.

Bug: 1007989
Change-Id: I59cddc51a65c9acd8e134845d7c9c4b6320fc4d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1864414Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Daniel Libby <dlibby@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#706973}

third_party/blink/renderer/core/clipboard/data_transfer.cc

@@ -123,8 +123,7 @@ class DraggedNodeImageBuilder {
     PaintLayerPaintingInfo painting_info(
         layer, CullRect(EnclosingIntRect(bounding_box)),
         kGlobalPaintFlattenCompositingLayers, PhysicalOffset());
-    PaintLayerFlags flags = kPaintLayerHaveTransparency |
-                            kPaintLayerUncachedClipRects;
+    PaintLayerFlags flags = kPaintLayerHaveTransparency;
     PaintRecordBuilder builder;
 
     dragged_layout_object->GetDocument().Lifecycle().AdvanceTo(

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

@@ -78,17 +78,6 @@ PaintResult PaintLayerPainter::Paint(
   // https://code.google.com/p/chromium/issues/detail?id=343772
   DisableCompositingQueryAsserts disabler;
 
-  if (paint_layer_.GetCompositingState() != kNotComposited) {
-    if (painting_info.GetGlobalPaintFlags() &
-        kGlobalPaintFlattenCompositingLayers) {
-      // FIXME: ok, but what about GlobalPaintFlattenCompositingLayers? That's
-      // for printing and drag-image.
-      // FIXME: why isn't the code here global, as opposed to being set on each
-      // paint() call?
-      paint_flags |= kPaintLayerUncachedClipRects;
-    }
-  }
-
   // Non self-painting layers without self-painting descendants don't need to be
   // painted as their layoutObject() should properly paint itself.
   if (!paint_layer_.IsSelfPaintingLayer() &&
@@ -146,8 +135,8 @@ static bool ShouldCreateSubsequence(const PaintLayer& paint_layer,
   if (painting_info.GetGlobalPaintFlags() &
       kGlobalPaintFlattenCompositingLayers)
     return false;
-  if (paint_flags & (kPaintLayerPaintingOverlayOverflowControls |
-                     kPaintLayerUncachedClipRects))
+
+  if (paint_flags & kPaintLayerPaintingOverlayOverflowControls)
     return false;
 
   return true;

third_party/blink/renderer/core/paint/paint_layer_painting_info.h

@@ -63,7 +63,6 @@ class PaintLayer;
 enum PaintLayerFlag {
   kPaintLayerNoFlag = 0,
   kPaintLayerHaveTransparency = 1,
-  kPaintLayerUncachedClipRects = 1 << 2,
   kPaintLayerPaintingOverlayOverflowControls = 1 << 3,
   kPaintLayerPaintingCompositingBackgroundPhase = 1 << 4,
   kPaintLayerPaintingCompositingForegroundPhase = 1 << 5,
@@ -137,8 +136,6 @@ inline String PaintLayerFlagsToDebugString(PaintLayerFlags flags) {
 
   if (flags & kPaintLayerHaveTransparency)
     append("kPaintLayerHaveTransparency");
-  if (flags & kPaintLayerUncachedClipRects)
-    append("kPaintLayerUncachedClipRects");
   if (flags & kPaintLayerPaintingOverlayOverflowControls)
     append("kPaintLayerPaintingOverlayOverflowControls");
   if (flags & kPaintLayerPaintingCompositingScrollingPhase)