Don't serialize SkPath::getGenerationID() identifiability digests.

These IDs introduce variance in digest values for the same set of canvas
2D context operations.

Also, add some unit test coverage that we were missing.

Bug: 973801
Change-Id: I12728c5ab4dcd46b6a21bbcfbb18066652ebbf93
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2243731
Commit-Queue: Caleb Raitto <caraitto@chromium.org>
Reviewed-by: Khushal <khushalsagar@chromium.org>
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792371}

cc/paint/paint_op_buffer.h

@@ -187,6 +187,13 @@ class CC_PAINT_EXPORT PaintOp {
     // The flags to use when serializing this op. This can be used to override
     // the flags serialized with the op. Valid only for PaintOpWithFlags.
     const PaintFlags* flags_to_serialize = nullptr;
+
+    // TODO(crbug.com/1096123): Cleanup after study completion.
+    //
+    // If true, perform serializaion in a way that avoids serializing transient
+    // members, such as IDs, so that a stable digest can be calculated. This
+    // means that serialized output can't be deserialized correctly.
+    bool for_identifiability_study = false;
   };
 
   struct CC_PAINT_EXPORT DeserializeOptions {

cc/paint/paint_op_writer.cc

@@ -174,7 +174,8 @@ void PaintOpWriter::Write(const SkRRect& rect) {
 
 void PaintOpWriter::Write(const SkPath& path) {
   auto id = path.getGenerationID();
-  Write(id);
+  if (!options_.for_identifiability_study)
+    Write(id);
 
   if (options_.paint_cache->Get(PaintCacheDataType::kPath, id)) {
     Write(static_cast<uint32_t>(PaintCacheEntryState::kCached));
@@ -511,7 +512,8 @@ void PaintOpWriter::Write(const PaintShader* shader, SkFilterQuality quality) {
   if (shader->record_) {
     Write(true);
     DCHECK_NE(shader->id_, PaintShader::kInvalidRecordShaderId);
-    Write(shader->id_);
+    if (!options_.for_identifiability_study)
+      Write(shader->id_);
     const gfx::Rect playback_rect(
         gfx::ToEnclosingRect(gfx::SkRectToRectF(shader->tile())));
 

third_party/blink/renderer/platform/BUILD.gn

@@ -1928,6 +1928,7 @@ jumbo_source_set("blink_platform_unittests_sources") {
     "graphics/gpu/webgpu_image_bitmap_handler_test.cc",
     "graphics/gpu/webgpu_swap_buffer_provider_test.cc",
     "graphics/graphics_context_test.cc",
+    "graphics/identifiability_paint_op_digest_unittest.cc",
     "graphics/lab_color_space_test.cc",
     "graphics/paint/cull_rect_test.cc",
     "graphics/paint/display_item_client_test.cc",

third_party/blink/renderer/platform/graphics/identifiability_paint_op_digest.cc

@@ -35,6 +35,7 @@ IdentifiabilityPaintOpDigest::IdentifiabilityPaintOpDigest(IntSize size)
                          /*content_supports_distance_field_text=*/false,
                          /*max_texture_size=*/0,
                          /*original_ctm=*/SkMatrix::I()) {
+  serialize_options_.for_identifiability_study = true;
   constexpr size_t kInitialSize = 16 * 1024;
   if (IsUserInIdentifiabilityStudy() &&
       SerializationBuffer().size() < kInitialSize)

third_party/blink/renderer/platform/graphics/identifiability_paint_op_digest.h

@@ -11,6 +11,7 @@
 #include "cc/paint/image_provider.h"
 #include "cc/paint/paint_cache.h"
 #include "third_party/blink/renderer/platform/geometry/int_size.h"
+#include "third_party/blink/renderer/platform/platform_export.h"
 #include "third_party/skia/include/utils/SkNoDrawCanvas.h"
 
 namespace blink {
@@ -19,7 +20,7 @@ namespace blink {
 // the serialization of PaintOps generated by those operations.
 //
 // TODO(crbug.com/973801): Report results poisoning when dropping PaintOps.
-class IdentifiabilityPaintOpDigest {
+class PLATFORM_EXPORT IdentifiabilityPaintOpDigest {
  public:
   // Constructs based on the size of the CanvasResourceProvider.
   explicit IdentifiabilityPaintOpDigest(IntSize size);

third_party/blink/renderer/platform/graphics/identifiability_paint_op_digest_unittest.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "third_party/blink/renderer/platform/graphics/identifiability_paint_op_digest.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/blink/public/common/privacy_budget/identifiability_study_settings.h"
+#include "third_party/blink/public/common/privacy_budget/identifiability_study_settings_provider.h"
+#include "third_party/skia/include/core/SkPath.h"
+#include "third_party/skia/include/core/SkTileMode.h"
+
+namespace blink {
+
+namespace {
+
+// A IdentifiabilityStudySettingsProvider implementation that opts-into study
+// participation.
+class ActiveSettingsProvider : public IdentifiabilityStudySettingsProvider {
+ public:
+  bool IsActive() const override { return true; }
+
+  // The following return values don't matter.
+  bool IsAnyTypeOrSurfaceBlocked() const override { return true; }
+  bool IsSurfaceAllowed(IdentifiableSurface surface) const override {
+    return false;
+  }
+  bool IsTypeAllowed(IdentifiableSurface::Type type) const override {
+    return false;
+  }
+};
+
+// An RAII class that opts into study participation using
+// ActiveSettingsProvider.
+class StudyParticipationRaii {
+ public:
+  StudyParticipationRaii() {
+    IdentifiabilityStudySettings::SetGlobalProvider(
+        std::make_unique<ActiveSettingsProvider>());
+  }
+  ~StudyParticipationRaii() {
+    IdentifiabilityStudySettings::ResetStateForTesting();
+  }
+};
+
+// Arbitrary non-zero size.
+constexpr IntSize kSize(10, 10);
+
+TEST(IdentifiabilityPaintOpDigestTest, Construct) {
+  IdentifiabilityPaintOpDigest identifiability_paintop_digest(kSize);
+}
+
+TEST(IdentifiabilityPaintOpDigestTest, Construct_InStudy) {
+  StudyParticipationRaii study_participation_raii;
+  IdentifiabilityPaintOpDigest identifiability_paintop_digest(kSize);
+}
+
+TEST(IdentifiabilityPaintOpDigestTest, InitialDigestIsZero) {
+  StudyParticipationRaii study_participation_raii;
+  IdentifiabilityPaintOpDigest identifiability_paintop_digest(kSize);
+  auto paint_record = sk_make_sp<cc::PaintRecord>();
+  identifiability_paintop_digest.MaybeUpdateDigest(paint_record,
+                                                   /*num_ops_to_visit=*/1);
+  EXPECT_EQ(UINT64_C(0), identifiability_paintop_digest.digest());
+}
+
+TEST(IdentifiabilityPaintOpDigestTest, SimpleDigest) {
+  StudyParticipationRaii study_participation_raii;
+  IdentifiabilityPaintOpDigest identifiability_paintop_digest(kSize);
+  auto paint_record = sk_make_sp<cc::PaintRecord>();
+  paint_record->push<cc::ScaleOp>(1.0f, 1.0f);
+  identifiability_paintop_digest.MaybeUpdateDigest(paint_record,
+                                                   /*num_ops_to_visit=*/1);
+  EXPECT_EQ(UINT64_C(5461154373811575393),
+            identifiability_paintop_digest.digest());
+}
+
+TEST(IdentifiabilityPaintOpDigestTest, DigestIsZeroIfNotInStudy) {
+  IdentifiabilityPaintOpDigest identifiability_paintop_digest(kSize);
+  auto paint_record = sk_make_sp<cc::PaintRecord>();
+  paint_record->push<cc::ScaleOp>(1.0f, 1.0f);
+  identifiability_paintop_digest.MaybeUpdateDigest(paint_record,
+                                                   /*num_ops_to_visit=*/1);
+  EXPECT_EQ(UINT64_C(0), identifiability_paintop_digest.digest());
+}
+
+TEST(IdentifiabilityPaintOpDigestTest, SkipsTextOps) {
+  StudyParticipationRaii study_participation_raii;
+  IdentifiabilityPaintOpDigest identifiability_paintop_digest(kSize);
+  auto paint_record = sk_make_sp<cc::PaintRecord>();
+  paint_record->push<cc::DrawTextBlobOp>(
+      SkTextBlob::MakeFromString("abc", SkFont(SkTypeface::MakeDefault())),
+      1.0f, 1.0f, cc::PaintFlags());
+  identifiability_paintop_digest.MaybeUpdateDigest(paint_record,
+                                                   /*num_ops_to_visit=*/1);
+  EXPECT_EQ(UINT64_C(0), identifiability_paintop_digest.digest());
+}
+
+TEST(IdentifiabilityPaintOpDigestTest, SkPathDigestStability) {
+  StudyParticipationRaii study_participation_raii;
+  // These 2 SkPath objects will have different internal generation IDs. We
+  // can't use empty paths as in that case the internal SkPathRefs (which holds
+  // the ID) for each SkPath would be the same global "empty" SkPathRef, so we
+  // make the SkPaths non-empty.
+  SkPath path1;
+  path1.rLineTo(1.0f, 0.0f);
+  SkPath path2;
+  path2.rLineTo(1.0f, 0.0f);
+  IdentifiabilityPaintOpDigest identifiability_paintop_digest1(kSize);
+  IdentifiabilityPaintOpDigest identifiability_paintop_digest2(kSize);
+  auto paint_record1 = sk_make_sp<cc::PaintRecord>();
+  auto paint_record2 = sk_make_sp<cc::PaintRecord>();
+  paint_record1->push<cc::DrawPathOp>(path1, cc::PaintFlags());
+  paint_record2->push<cc::DrawPathOp>(path2, cc::PaintFlags());
+  identifiability_paintop_digest1.MaybeUpdateDigest(paint_record1,
+                                                    /*num_ops_to_visit=*/1);
+  identifiability_paintop_digest2.MaybeUpdateDigest(paint_record2,
+                                                    /*num_ops_to_visit=*/1);
+  EXPECT_EQ(identifiability_paintop_digest1.digest(),
+            identifiability_paintop_digest2.digest());
+  EXPECT_EQ(UINT64_C(154630961637231072),
+            identifiability_paintop_digest1.digest());
+}
+
+TEST(IdentifiabilityPaintOpDigestTest, PaintShaderStability) {
+  StudyParticipationRaii study_participation_raii;
+  SkPath path;
+  path.rLineTo(1.0f, 0.0f);
+  IdentifiabilityPaintOpDigest identifiability_paintop_digest1(kSize);
+  IdentifiabilityPaintOpDigest identifiability_paintop_digest2(kSize);
+  auto paint_record1 = sk_make_sp<cc::PaintRecord>();
+  auto paint_record2 = sk_make_sp<cc::PaintRecord>();
+  auto paint_record_shader = sk_make_sp<cc::PaintRecord>();
+  paint_record_shader->push<cc::ScaleOp>(2.0f, 2.0f);
+  const SkRect tile = SkRect::MakeWH(100, 100);
+  // These 2 shaders will have different internal generation IDs.
+  cc::PaintFlags paint_flags1;
+  paint_flags1.setShader(cc::PaintShader::MakePaintRecord(
+      paint_record_shader, tile, SkTileMode::kClamp, SkTileMode::kClamp,
+      nullptr));
+  cc::PaintFlags paint_flags2;
+  paint_flags2.setShader(cc::PaintShader::MakePaintRecord(
+      paint_record_shader, tile, SkTileMode::kClamp, SkTileMode::kClamp,
+      nullptr));
+  paint_record1->push<cc::DrawPathOp>(path, paint_flags1);
+  paint_record2->push<cc::DrawPathOp>(path, paint_flags2);
+  identifiability_paintop_digest1.MaybeUpdateDigest(paint_record1,
+                                                    /*num_ops_to_visit=*/1);
+  identifiability_paintop_digest2.MaybeUpdateDigest(paint_record2,
+                                                    /*num_ops_to_visit=*/1);
+  EXPECT_EQ(identifiability_paintop_digest1.digest(),
+            identifiability_paintop_digest2.digest());
+  EXPECT_EQ(UINT64_C(4893847605848349986),
+            identifiability_paintop_digest1.digest());
+}
+
+}  // namespace
+
+}  // namespace blink