Optimize SourceLocation::Capture

Determining the v8::Isolate can take ~25% of the time
required to capture the top of the stack. This CL gets the Isolate
from the ExecutionContext when it's available to speed things up.

Bug: 851531
Change-Id: Ia823fbb0643c62f1a4da3cc289b23ca6fb43da2b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2122568
Commit-Queue: Josh Karlin <jkarlin@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#754054}

third_party/blink/renderer/bindings/core/v8/source_location.cc

@@ -23,15 +23,17 @@ namespace blink {
 
 namespace {
 
-std::unique_ptr<v8_inspector::V8StackTrace> CaptureStackTrace(bool full) {
-  v8::Isolate* isolate = v8::Isolate::GetCurrent();
+std::unique_ptr<v8_inspector::V8StackTrace> CaptureStackTrace(
+    v8::Isolate* isolate,
+    bool full) {
   ThreadDebugger* debugger = ThreadDebugger::From(isolate);
   if (!debugger || !isolate->InContext())
     return nullptr;
   ScriptForbiddenScope::AllowUserAgentScript allow_scripting;
   return debugger->GetV8Inspector()->captureStackTrace(full);
 }
-}
+
+}  // namespace
 
 // static
 std::unique_ptr<SourceLocation> SourceLocation::Capture(
@@ -39,7 +41,7 @@ std::unique_ptr<SourceLocation> SourceLocation::Capture(
     unsigned line_number,
     unsigned column_number) {
   std::unique_ptr<v8_inspector::V8StackTrace> stack_trace =
-      CaptureStackTrace(false);
+      CaptureStackTrace(v8::Isolate::GetCurrent(), false);
   if (stack_trace && !stack_trace->isEmpty())
     return SourceLocation::CreateFromNonEmptyV8StackTrace(
         std::move(stack_trace), 0);
@@ -50,8 +52,14 @@ std::unique_ptr<SourceLocation> SourceLocation::Capture(
 // static
 std::unique_ptr<SourceLocation> SourceLocation::Capture(
     ExecutionContext* execution_context) {
+  // v8::Isolate::GetCurrent is slow so get it from the ExecutionContext when
+  // available.
+  // TODO(jkarlin): Force all callers of all Capture() methods to call with a
+  // valid ExecutionContext.
+  v8::Isolate* isolate = execution_context ? execution_context->GetIsolate()
+                                           : v8::Isolate::GetCurrent();
   std::unique_ptr<v8_inspector::V8StackTrace> stack_trace =
-      CaptureStackTrace(false);
+      CaptureStackTrace(isolate, false);
   if (stack_trace && !stack_trace->isEmpty())
     return SourceLocation::CreateFromNonEmptyV8StackTrace(
         std::move(stack_trace), 0);
@@ -137,7 +145,7 @@ std::unique_ptr<SourceLocation> SourceLocation::FromFunction(
 // static
 std::unique_ptr<SourceLocation> SourceLocation::CaptureWithFullStackTrace() {
   std::unique_ptr<v8_inspector::V8StackTrace> stack_trace =
-      CaptureStackTrace(true);
+      CaptureStackTrace(v8::Isolate::GetCurrent(), true);
   if (stack_trace && !stack_trace->isEmpty())
     return SourceLocation::CreateFromNonEmptyV8StackTrace(
         std::move(stack_trace), 0);