[coverage] Provide option to prevent triggered updates

Coverage updates are sent as deltas, and this means that it
is very important that the consumer gets /all/ updates;
otherwise, the coverage information will be wrong.

Previously, we introduces the ability into the back-end to
send triggered updates, i.e. updates that are triggered by
the back-end at interesting points in time. These updates
are delivered via an event, and any consumer must process
these events.

This CL introduces a flag to startPreciseCoverage that
controls whether the back-end is allowed to send such
triggered updates on its own initiative. The default is
`false` to maintain backwards compatibility with consumers
that don't yet handle the events.

Bug: chromium:1022031
Change-Id: Ie36a92a3b627b19ea4041f1b8da1ec66c6b9b771
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2043798Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66232}

include/js_protocol.pdl

@@ -831,6 +831,8 @@ domain Profiler
       optional boolean callCount
       # Collect block-based coverage.
       optional boolean detailed
+      # Allow the backend to send updates on its own initiative
+      optional boolean allowTriggeredUpdates
     returns
       # Monotonically increasing time (in seconds) when the coverage update was taken in the backend.
       number timestamp

src/inspector/v8-profiler-agent-impl.cc

@@ -27,8 +27,10 @@ static const char profilerEnabled[] = "profilerEnabled";
 static const char preciseCoverageStarted[] = "preciseCoverageStarted";
 static const char preciseCoverageCallCount[] = "preciseCoverageCallCount";
 static const char preciseCoverageDetailed[] = "preciseCoverageDetailed";
+static const char preciseCoverageAllowTriggeredUpdates[] =
+    "preciseCoverageAllowTriggeredUpdates";
 static const char typeProfileStarted[] = "typeProfileStarted";
-}
+}  // namespace ProfilerAgentState
 
 namespace {
 
@@ -261,9 +263,11 @@ void V8ProfilerAgentImpl::restore() {
         ProfilerAgentState::preciseCoverageCallCount, false);
     bool detailed = m_state->booleanProperty(
         ProfilerAgentState::preciseCoverageDetailed, false);
+    bool updatesAllowed = m_state->booleanProperty(
+        ProfilerAgentState::preciseCoverageAllowTriggeredUpdates, false);
     double timestamp;
     startPreciseCoverage(Maybe<bool>(callCount), Maybe<bool>(detailed),
-                         &timestamp);
+                         Maybe<bool>(updatesAllowed), &timestamp);
   }
 }
 
@@ -294,19 +298,22 @@ Response V8ProfilerAgentImpl::stop(
   return Response::OK();
 }
 
-Response V8ProfilerAgentImpl::startPreciseCoverage(Maybe<bool> callCount,
-                                                   Maybe<bool> detailed,
-                                                   double* out_timestamp) {
+Response V8ProfilerAgentImpl::startPreciseCoverage(
+    Maybe<bool> callCount, Maybe<bool> detailed,
+    Maybe<bool> allowTriggeredUpdates, double* out_timestamp) {
   if (!m_enabled) return Response::Error("Profiler is not enabled");
   *out_timestamp =
       v8::base::TimeTicks::HighResolutionNow().since_origin().InSecondsF();
   bool callCountValue = callCount.fromMaybe(false);
   bool detailedValue = detailed.fromMaybe(false);
+  bool allowTriggeredUpdatesValue = allowTriggeredUpdates.fromMaybe(false);
   m_state->setBoolean(ProfilerAgentState::preciseCoverageStarted, true);
   m_state->setBoolean(ProfilerAgentState::preciseCoverageCallCount,
                       callCountValue);
   m_state->setBoolean(ProfilerAgentState::preciseCoverageDetailed,
                       detailedValue);
+  m_state->setBoolean(ProfilerAgentState::preciseCoverageAllowTriggeredUpdates,
+                      allowTriggeredUpdatesValue);
   // BlockCount is a superset of PreciseCount. It includes block-granularity
   // coverage data if it exists (at the time of writing, that's the case for
   // each function recompiled after the BlockCount mode has been set); and
@@ -420,6 +427,10 @@ void V8ProfilerAgentImpl::triggerPreciseCoverageDeltaUpdate(
                                 false)) {
     return;
   }
+  if (!m_state->booleanProperty(
+          ProfilerAgentState::preciseCoverageAllowTriggeredUpdates, false)) {
+    return;
+  }
   v8::HandleScope handle_scope(m_isolate);
   v8::debug::Coverage coverage = v8::debug::Coverage::CollectPrecise(m_isolate);
   std::unique_ptr<protocol::Array<protocol::Profiler::ScriptCoverage>>

src/inspector/v8-profiler-agent-impl.h

@@ -40,6 +40,7 @@ class V8ProfilerAgentImpl : public protocol::Profiler::Backend {
   Response stop(std::unique_ptr<protocol::Profiler::Profile>*) override;
 
   Response startPreciseCoverage(Maybe<bool> binary, Maybe<bool> detailed,
+                                Maybe<bool> allow_triggered_updates,
                                 double* out_timestamp) override;
   Response stopPreciseCoverage() override;
   Response takePreciseCoverage(