Remove unused CaptureStartTime() calls from PerformanceMonitor

The only usage of |v8_compile_start_time_| was removed in commit 5214e811
and the only usage of CaptureStartTime() and Duration() for
probe::ExecuteScript was also removed by that commit. Therefore, the
member can be removed and the call to CaptureStartTime() can be removed.

Bug: 738493
Change-Id: I8f59ba31fd1d64bfba40ec3e3e07f80940253864
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1872775Reviewed-by: Steve Kobes <skobes@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708311}

third_party/blink/renderer/core/frame/performance_monitor.cc

@@ -188,8 +188,6 @@ void PerformanceMonitor::Did(const probe::UpdateLayout& probe) {
 
 void PerformanceMonitor::Will(const probe::ExecuteScript& probe) {
   WillExecuteScript(probe.context);
-
-  probe.CaptureStartTime();
 }
 
 void PerformanceMonitor::Did(const probe::ExecuteScript& probe) {
@@ -227,10 +225,6 @@ void PerformanceMonitor::Did(const probe::CallFunction& probe) {
 
 void PerformanceMonitor::Will(const probe::V8Compile& probe) {
   UpdateTaskAttribution(probe.context);
-  if (!enabled_ || thresholds_[kLongTask].is_zero())
-    return;
-
-  v8_compile_start_time_ = probe.CaptureStartTime();
 }
 
 void PerformanceMonitor::Did(const probe::V8Compile& probe) {}
@@ -276,7 +270,6 @@ void PerformanceMonitor::WillProcessTask(base::TimeTicks start_time) {
   layout_depth_ = 0;
   per_task_style_and_layout_time_ = base::TimeDelta();
   user_callback_ = nullptr;
-  v8_compile_start_time_ = base::TimeTicks();
 }
 
 void PerformanceMonitor::DidProcessTask(base::TimeTicks start_time,

third_party/blink/renderer/core/frame/performance_monitor.h

@@ -142,7 +142,6 @@ class CORE_EXPORT PerformanceMonitor final
   unsigned layout_depth_ = 0;
   unsigned user_callback_depth_ = 0;
   const void* user_callback_;
-  base::TimeTicks v8_compile_start_time_;
 
   base::TimeDelta thresholds_[kAfterLast];