DNR: Add UMA for initiator checks performed by the page whitelisting API.

The Declarative Net Request Page Whitelisting API uses initiator checks to guess
the main frame url for a main-frame subresource request. This CL adds UMA to
enumerate how often the different cases occur. This should help reason about the
correctness of these checks.

BUG=811460

Change-Id: Id72c05041477d05825fbe7e0ff7fecbf39fda861
Reviewed-on: https://chromium-review.googlesource.com/1089475Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565473}

extensions/browser/api/declarative_net_request/ruleset_manager.cc

@@ -30,6 +30,19 @@ namespace {
 
 namespace flat_rule = url_pattern_index::flat;
 
+// Describes the different cases pertaining to initiator checks to find the main
+// frame url for a main frame subresource.
+// These values are persisted to logs. Entries should not be renumbered and
+// numeric values should never be reused.
+enum class PageWhitelistingInitiatorCheck {
+  kInitiatorAbsent = 0,
+  kNeitherCandidateMatchesInitiator = 1,
+  kCommittedCandidateMatchesInitiator = 2,
+  kPendingCandidateMatchesInitiator = 3,
+  kBothCandidatesMatchInitiator = 4,
+  kMaxValue = kBothCandidatesMatchInitiator,
+};
+
 // Maps content::ResourceType to flat_rule::ElementType.
 flat_rule::ElementType GetElementType(content::ResourceType type) {
   switch (type) {
@@ -160,6 +173,12 @@ bool IsRequestPageWhitelisted(const WebRequestInfo& request,
   // loads.
   DCHECK_EQ(ExtensionApiFrameIdMap::kTopFrameId, request.frame_data->frame_id);
 
+  auto log_uma = [](PageWhitelistingInitiatorCheck value) {
+    UMA_HISTOGRAM_ENUMERATION(
+        "Extensions.DeclarativeNetRequest.PageWhitelistingInitiatorCheck",
+        value);
+  };
+
   // At this point, we are evaluating a main-frame subresource. There are two
   // candidate main frame urls - |pending_main_frame_url| and
   // |last_committed_main_frame_url|. To predict the correct main frame url,
@@ -167,7 +186,9 @@ bool IsRequestPageWhitelisted(const WebRequestInfo& request,
   // of the main frame in this case) with the candidate urls' origins. If only
   // one of the candidate url's origin matches the request initiator, we can be
   // reasonably sure that it is the correct main frame url.
-  if (request.initiator) {
+  if (!request.initiator) {
+    log_uma(PageWhitelistingInitiatorCheck::kInitiatorAbsent);
+  } else {
     const bool initiator_matches_pending_url =
         url::Origin::Create(*request.frame_data->pending_main_frame_url) ==
         *request.initiator;
@@ -178,6 +199,8 @@ bool IsRequestPageWhitelisted(const WebRequestInfo& request,
 
     if (initiator_matches_pending_url && !initiator_matches_committed_url) {
       // We predict that |pending_main_frame_url| is the actual main frame url.
+      log_uma(
+          PageWhitelistingInitiatorCheck::kPendingCandidateMatchesInitiator);
       return whitelisted_pages.MatchesURL(
           *request.frame_data->pending_main_frame_url);
     }
@@ -185,16 +208,26 @@ bool IsRequestPageWhitelisted(const WebRequestInfo& request,
     if (initiator_matches_committed_url && !initiator_matches_pending_url) {
       // We predict that |last_committed_main_frame_url| is the actual main
       // frame url.
+      log_uma(
+          PageWhitelistingInitiatorCheck::kCommittedCandidateMatchesInitiator);
       return whitelisted_pages.MatchesURL(
           request.frame_data->last_committed_main_frame_url);
     }
+
+    if (initiator_matches_pending_url && initiator_matches_committed_url) {
+      log_uma(PageWhitelistingInitiatorCheck::kBothCandidatesMatchInitiator);
+    } else {
+      DCHECK(!initiator_matches_pending_url);
+      DCHECK(!initiator_matches_committed_url);
+      log_uma(
+          PageWhitelistingInitiatorCheck::kNeitherCandidateMatchesInitiator);
+    }
   }
 
   // If we are not able to correctly predict the main frame url, simply test
   // against both the possible URLs. This means a small proportion of main frame
   // subresource requests might be incorrectly whitelisted by the page
   // whitelisting API.
-  // TODO(karandeepb): Add UMA to see how often this happens.
   return whitelisted_pages.MatchesURL(
              request.frame_data->last_committed_main_frame_url) ||
          whitelisted_pages.MatchesURL(

tools/metrics/histograms/enums.xml

@@ -35129,6 +35129,14 @@ Called by update_net_trust_anchors.py.-->
   <int value="8" label="Unknown"/>
 </enum>
 
+<enum name="PageWhitelistingInitiatorCheck">
+  <int value="0" label="Initiator absent"/>
+  <int value="1" label="Neither candidate matches initiator"/>
+  <int value="2" label="Committed candidate matches initiator"/>
+  <int value="3" label="Pending candidate matches initiator"/>
+  <int value="4" label="Both candidates match initiator"/>
+</enum>
+
 <enum name="PaletteModeCancelType">
   <int value="0" label="Palette laser pointer mode is cancelled."/>
   <int value="1" label="Palette laser pointer mode is switched out of"/>

tools/metrics/histograms/histograms.xml

@@ -26283,6 +26283,18 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram
+    name="Extensions.DeclarativeNetRequest.PageWhitelistingInitiatorCheck"
+    enum="PageWhitelistingInitiatorCheck" expires_after="2019-06-30">
+  <owner>karandeepb@chromium.org</owner>
+  <owner>lazyboy@chromium.org</owner>
+  <summary>
+    Describes the different cases pertaining to initiator checks used by the
+    Declarative Net Request Page Whitelisting API. Emitted whenever an extension
+    ruleset is evaluated for a main frame sub-resource request.
+  </summary>
+</histogram>
+
 <histogram
     name="Extensions.DeclarativeNetRequest.ShouldBlockRequestTime.AllExtensions"
     units="ms">