[DL]: Add async traces to indicate when the lock is acquired and in what state.

This patch adds some trace information to Display locking to allow
keeping track of display lock state in traces.

R=chrishtr@chromium.org, rakina@chromium.org

Bug: 882663
Change-Id: I1e67370ab06b6eebda6efed0e8e3870cdc4bfc2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504163Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Commit-Queue: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638159}

third_party/blink/renderer/core/display_lock/display_lock_context.cc

@@ -4,6 +4,8 @@
 
 #include "third_party/blink/renderer/core/display_lock/display_lock_context.h"
 
+#include <string>
+
 #include "base/memory/ptr_util.h"
 #include "third_party/blink/renderer/core/display_lock/display_lock_options.h"
 #include "third_party/blink/renderer/core/display_lock/strict_yielding_display_lock_budget.h"
@@ -37,6 +39,24 @@ const char* kElementIsDisconnected = "Element is disconnected.";
 const char* kLockCommitted = "Lock commit was requested.";
 }  // namespace rejection_names
 
+// Helper function to convert a display locking state to a string. Used in
+// traces.
+std::string StateToString(DisplayLockContext::State state) {
+  switch (state) {
+    case DisplayLockContext::kLocked:
+      return "kLocked";
+    case DisplayLockContext::kUpdating:
+      return "kUpdating";
+    case DisplayLockContext::kCommitting:
+      return "kCommitting";
+    case DisplayLockContext::kUnlocked:
+      return "kUnlocked";
+    case DisplayLockContext::kPendingAcquire:
+      return "kPendingAcquire";
+  }
+  return "";
+}
+
 // Helper function that returns an immediately rejected promise.
 ScriptPromise GetRejectedPromise(ScriptState* script_state,
                                  const char* rejection_reason) {
@@ -120,6 +140,7 @@ bool DisplayLockContext::HasPendingActivity() const {
 
 ScriptPromise DisplayLockContext::acquire(ScriptState* script_state,
                                           DisplayLockOptions* options) {
+  TRACE_EVENT0("blink", "DisplayLockContext::acquire()");
   double timeout_ms = (options && options->hasTimeout())
                           ? options->timeout()
                           : kDefaultLockTimeoutMs;
@@ -167,6 +188,7 @@ ScriptPromise DisplayLockContext::acquire(ScriptState* script_state,
 }
 
 ScriptPromise DisplayLockContext::update(ScriptState* script_state) {
+  TRACE_EVENT0("blink", "DisplayLockContext::update()");
   // Reject if we're unlocked or disconnected.
   if (state_ == kUnlocked || state_ == kPendingAcquire ||
       !element_->isConnected()) {
@@ -187,6 +209,7 @@ ScriptPromise DisplayLockContext::update(ScriptState* script_state) {
 }
 
 ScriptPromise DisplayLockContext::commit(ScriptState* script_state) {
+  TRACE_EVENT0("blink", "DisplayLockContext::commit()");
   // Resolve if we're already unlocked.
   if (state_ == kUnlocked)
     return GetResolvedPromise(script_state);
@@ -214,6 +237,8 @@ ScriptPromise DisplayLockContext::commit(ScriptState* script_state) {
 }
 
 ScriptPromise DisplayLockContext::updateAndCommit(ScriptState* script_state) {
+  TRACE_EVENT0("blink", "DisplayLockContext::updateAndCommit()");
+
   // Resolve if we're already unlocked.
   if (state_ == kUnlocked)
     return GetResolvedPromise(script_state);
@@ -802,10 +827,20 @@ operator=(State new_state) {
   if (new_state == state_)
     return *this;
 
+  if (state_ == kUnlocked) {
+    TRACE_EVENT_ASYNC_BEGIN0("blink", "LockedDisplayLock", this);
+  } else if (new_state == kUnlocked) {
+    TRACE_EVENT_ASYNC_END0("blink", "LockedDisplayLock", this);
+  }
+
   bool was_activatable = context_->IsActivatable();
   bool was_locked = context_->IsLocked();
 
   state_ = new_state;
+  if (state_ != kUnlocked) {
+    TRACE_EVENT_ASYNC_STEP_INTO0("blink", "LockedDisplayLock", this,
+                                 StateToString(state_));
+  }
 
   if (!context_->document_)
     return *this;

third_party/blink/renderer/core/display_lock/display_lock_context.h

@@ -50,6 +50,15 @@ class CORE_EXPORT DisplayLockContext final
     kDefault = kYieldBetweenLifecyclePhases
   };
 
+  // The current state of the lock. Note that the order of these matters.
+  enum State {
+    kLocked,
+    kUpdating,
+    kCommitting,
+    kUnlocked,
+    kPendingAcquire,
+  };
+
   // See GetScopedPendingFrameRect() for description.
   class ScopedPendingFrameRect {
     STACK_ALLOCATED();
@@ -162,15 +171,6 @@ class CORE_EXPORT DisplayLockContext final
   friend class DisplayLockSuspendedHandle;
   friend class DisplayLockBudget;
 
-  // The current state of the lock. Note that the order of these matters.
-  enum State {
-    kLocked,
-    kUpdating,
-    kCommitting,
-    kUnlocked,
-    kPendingAcquire,
-  };
-
   class StateChangeHelper {
     DISALLOW_NEW();