[PM] Create BoostingVoteAggregator.

Creates another VoteAggregator class that allows expressing "priority
boosting" votes, which can be used to resolve priority inversions.

BUG=971272

Change-Id: If84f0a7a22598de5f7a8897eb12066fbc5a00ccb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1853867Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Commit-Queue: Chris Hamilton <chrisha@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713958}

components/performance_manager/BUILD.gn

@@ -4,6 +4,7 @@
 
 static_library("performance_manager") {
   sources = [
+    "frame_priority/boosting_vote_aggregator.cc",
     "frame_priority/frame_priority.cc",
     "frame_priority/max_vote_aggregator.cc",
     "frame_priority/override_vote_aggregator.cc",
@@ -47,6 +48,7 @@ static_library("performance_manager") {
     "performance_manager_tab_helper.h",
     "process_node_source.cc",
     "process_node_source.h",
+    "public/frame_priority/boosting_vote_aggregator.h",
     "public/frame_priority/frame_priority.h",
     "public/frame_priority/max_vote_aggregator.h",
     "public/frame_priority/override_vote_aggregator.h",
@@ -87,6 +89,7 @@ source_set("unit_tests") {
   testonly = true
 
   sources = [
+    "frame_priority/boosting_vote_aggregator_unittest.cc",
     "frame_priority/frame_priority_unittest.cc",
     "frame_priority/max_vote_aggregator_unittest.cc",
     "frame_priority/override_vote_aggregator_unittest.cc",

components/performance_manager/test_support/frame_priority.cc

@@ -53,6 +53,13 @@ void DummyVoteConsumer::VoteInvalidated(AcceptedVote* vote) {
   --valid_vote_count_;
 }
 
+void DummyVoteConsumer::ExpectInvalidVote(size_t index) {
+  EXPECT_LT(index, votes_.size());
+  const AcceptedVote& accepted_vote = votes_[index];
+  EXPECT_EQ(this, accepted_vote.consumer());
+  EXPECT_FALSE(accepted_vote.IsValid());
+}
+
 void DummyVoteConsumer::ExpectValidVote(size_t index,
                                         VoterId voter_id,
                                         const FrameNode* frame_node,

components/performance_manager/test_support/frame_priority.h

@@ -28,6 +28,8 @@ class DummyVoteConsumer : public VoteConsumer {
                          const Vote& new_vote) override;
   void VoteInvalidated(AcceptedVote* vote) override;
 
+  void ExpectInvalidVote(size_t index);
+
   // Checks that the vote at position |index| is valid, and has the
   // corresponding |voter|, |frame_node| and |priority|. If |reason| is non-null
   // then it will be validated as well.