[SPv175+] Don't create transform operations for identity transforms

This avoids many extra Save/Transform(identity)/../Restore,
Save/../Restore without transform. Also simplifies
Save/ClipRect/Transform(identity)/Save/ClipRect/Transform/../Restore/Restore
to Save/ClipRect(combined)/Transform/../Restore.

This especially fixes the performance regression of perf tests containing
svg images.

https://pinpoint-dot-chromeperf.appspot.com/results2/16c651cec40000
shows 18% improvement of frame_time of
tough_canvas_cases/rendering_throughput/bouncing_svg_images.html.

Bug: 823452
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I4576646cbe9c59bc8a7f56b67ef59f2ad57f159d
Reviewed-on: https://chromium-review.googlesource.com/1020152
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Tien-Ren Chen <trchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552511}

third_party/blink/renderer/platform/graphics/compositing/paint_chunks_to_cc_layer.cc

@@ -132,7 +132,9 @@ class ConversionContext {
   void ApplyTransform(const TransformPaintPropertyNode* target_transform) {
     if (target_transform == current_transform_)
       return;
-    cc_list_.push<cc::ConcatOp>(GetSkMatrix(target_transform));
+    auto sk_matrix = GetSkMatrix(target_transform);
+    if (!sk_matrix.isIdentity())
+      cc_list_.push<cc::ConcatOp>(sk_matrix);
   }
 
   SkMatrix GetSkMatrix(
@@ -319,8 +321,12 @@ void ConversionContext::SwitchToClip(const ClipPaintPropertyNode* target_clip) {
     bool has_rounded_clip_or_clip_path =
         sub_clip->ClipRect().IsRounded() || sub_clip->ClipPath();
     if (!has_rounded_clip_or_clip_path && pending_combined_clip_rect &&
-        sub_clip->Parent()->LocalTransformSpace() ==
-            sub_clip->LocalTransformSpace()) {
+        (sub_clip->Parent()->LocalTransformSpace() ==
+             sub_clip->LocalTransformSpace() ||
+         GeometryMapper::SourceToDestinationProjection(
+             sub_clip->Parent()->LocalTransformSpace(),
+             sub_clip->LocalTransformSpace())
+             .IsIdentity())) {
       // Continue to combine rectangular clips in the same transform space.
       pending_combined_clip_rect->Intersect(sub_clip->ClipRect().Rect());
       lowest_combined_clip_node = sub_clip;
@@ -605,10 +611,16 @@ void ConversionContext::SwitchToTransform(
     return;
 
   EndTransform();
+  if (target_transform == current_transform_)
+    return;
+
+  auto sk_matrix = GetSkMatrix(target_transform);
+  if (sk_matrix.isIdentity())
+    return;
 
   cc_list_.StartPaint();
   cc_list_.push<cc::SaveOp>();
-  ApplyTransform(target_transform);
+  cc_list_.push<cc::ConcatOp>(sk_matrix);
   cc_list_.EndPaintOfPairedBegin();
   previous_transform_ = current_transform_;
   current_transform_ = target_transform;

third_party/blink/renderer/platform/graphics/compositing/paint_chunks_to_cc_layer_test.cc

@@ -829,5 +829,42 @@ TEST_F(PaintChunksToCcLayerTest, ChunksSamePropertyTreeState) {
                    cc::PaintOpType::Restore}));  // </c1></t1>
 }
 
+TEST_F(PaintChunksToCcLayerTest, NoOpForIdentityTransforms) {
+  auto t1 = CreateTransform(t0(), TransformationMatrix());
+  auto t2 = CreateTransform(t1.get(), TransformationMatrix());
+  auto t3 = CreateTransform(t2.get(), TransformationMatrix());
+  auto c1 =
+      ClipPaintPropertyNode::Create(c0(), t2, FloatRoundedRect(0, 0, 100, 100));
+  auto c2 =
+      ClipPaintPropertyNode::Create(c1, t3, FloatRoundedRect(0, 0, 200, 50));
+
+  TestChunks chunks;
+  chunks.AddChunk(t0(), c0(), e0());
+  chunks.AddChunk(t1.get(), c0(), e0());
+  chunks.AddChunk(t0(), c0(), e0());
+  chunks.AddChunk(t1.get(), c0(), e0());
+  chunks.AddChunk(t2.get(), c0(), e0());
+  chunks.AddChunk(t1.get(), c0(), e0());
+  chunks.AddChunk(t1.get(), c2.get(), e0());
+
+  auto output =
+      PaintChunksToCcLayer::Convert(
+          chunks.chunks, PropertyTreeState(t0(), c0(), e0()), gfx::Vector2dF(),
+          chunks.items, cc::DisplayItemList::kToBeReleasedAsPaintOpBuffer)
+          ->ReleaseAsRecord();
+
+  EXPECT_THAT(*output,
+              PaintRecordMatcher::Make(
+                  {cc::PaintOpType::DrawRecord,                       // <p0/>
+                   cc::PaintOpType::DrawRecord,                       // <p1/>
+                   cc::PaintOpType::DrawRecord,                       // <p2/>
+                   cc::PaintOpType::DrawRecord,                       // <p3/>
+                   cc::PaintOpType::DrawRecord,                       // <p4/>
+                   cc::PaintOpType::DrawRecord,                       // <p5/>
+                   cc::PaintOpType::Save, cc::PaintOpType::ClipRect,  // <c1+c2>
+                   cc::PaintOpType::DrawRecord,                       // <p6/>
+                   cc::PaintOpType::Restore}));  // </c1+c2>
+}
+
 }  // namespace
 }  // namespace blink