Remove DCHECK()s in ExecuteScriptsWaitingForLoad()

Previously, HTMLParserScriptRunner::ExecuteScriptsWaitingForLoad()
required the given PendingScript is still the valid
ParserBlockingScript().
However, this isn't the case when
HTMLParserScriptRunner::ExecuteParsingBlockingScripts()
is called after PendingScriptFinished() before NotifyScriptLoaded(),
because the PendingScript is already evaluated and
is no longer parser blocking.

This CL allows ExecuteScriptsWaitingForLoad() to be called
even when the finished PendingScript doesn't match with
ParserBlockingScript() or even when there are no longer
ParserBlockingScript(),
by removing DCHECK()s and |pending_script| argument.

This is safe because:
- All necessary conditions for evaluation
  is checked in ExecuteParsingBlockingScripts(),
  and extra stale calls to ExecuteParsingBlockingScripts()
  (i.e. called when parser blocking scripts are not ready)
  are ignored.
- |pending_script| hasn't been used other than for DCHECK()s.

Bug: 1093051
Change-Id: I921f8d8f1fc261547fa214822f75341de03c8cba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2239770
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789864}

third_party/blink/renderer/core/html/parser/html_document_parser.cc

@@ -1394,7 +1394,7 @@ void HTMLDocumentParser::AppendCurrentInputStreamToPreloadScannerAndScan() {
   ScanAndPreload(preload_scanner_.get());
 }
 
-void HTMLDocumentParser::NotifyScriptLoaded(PendingScript* pending_script) {
+void HTMLDocumentParser::NotifyScriptLoaded() {
   TRACE_EVENT1("blink", "HTMLDocumentParser::NotifyScriptLoaded", "parser",
                (void*)this);
   DCHECK(script_runner_);
@@ -1412,7 +1412,7 @@ void HTMLDocumentParser::NotifyScriptLoaded(PendingScript* pending_script) {
     return;
   }
 
-  script_runner_->ExecuteScriptsWaitingForLoad(pending_script);
+  script_runner_->ExecuteScriptsWaitingForLoad();
   if (!IsPaused())
     ResumeParsingAfterPause();
 }

third_party/blink/renderer/core/html/parser/html_document_parser.h

@@ -168,7 +168,7 @@ class CORE_EXPORT HTMLDocumentParser : public ScriptableDocumentParser,
   void DocumentElementAvailable() override;
 
   // HTMLParserScriptRunnerHost
-  void NotifyScriptLoaded(PendingScript*) final;
+  void NotifyScriptLoaded() final;
   HTMLInputStream& InputStream() final { return input_; }
   bool HasPreloadScanner() const final {
     return preload_scanner_.get() && !CanParseAsynchronously();

third_party/blink/renderer/core/script/html_parser_script_runner.cc

@@ -311,8 +311,7 @@ void HTMLParserScriptRunner::PendingScriptFinished(
   document_->GetTaskRunner(TaskType::kInternalContinueScriptLoading)
       ->PostTask(FROM_HERE,
                  WTF::Bind(&HTMLParserScriptRunnerHost::NotifyScriptLoaded,
-                           WrapPersistent(host_.Get()),
-                           WrapPersistent(pending_script)));
+                           WrapPersistent(host_.Get())));
 }
 
 // <specdef href="https://html.spec.whatwg.org/C/#scriptEndTag">
@@ -380,11 +379,20 @@ void HTMLParserScriptRunner::ExecuteParsingBlockingScripts() {
   // that is blocking scripts and the script's "ready to be parser-executed"
   // flag is set.</spec>
   //
-  // These conditions correspond to isParserBlockingScriptReady() and
-  // if it is false, executeParsingBlockingScripts() will be called later
-  // when isParserBlockingScriptReady() becomes true:
-  // (1) from HTMLParserScriptRunner::executeScriptsWaitingForResources(), or
-  // (2) from HTMLParserScriptRunner::executeScriptsWaitingForLoad().
+  // These conditions correspond to IsParserBlockingScriptReady().
+  // If it is false at the time of #prepare-a-script,
+  // ExecuteParsingBlockingScripts() will be called later
+  // when IsParserBlockingScriptReady() might become true:
+  // - Called from HTMLParserScriptRunner::ExecuteScriptsWaitingForResources()
+  //   when the parser's Document has no style sheet that is blocking scripts,
+  // - Called from HTMLParserScriptRunner::ExecuteScriptsWaitingForLoad()
+  //   when the script's "ready to be parser-executed" flag is set, or
+  // - Other cases where any of the conditions isn't met or even when there are
+  //   no longer parser blocking scripts at all.
+  //   (For example, see the comment in ExecuteScriptsWaitingForLoad())
+  //
+  // Because we check the conditions below and do nothing if the conditions
+  // aren't met, it's safe to have extra ExecuteParsingBlockingScripts() calls.
   while (HasParserBlockingScript() && IsParserBlockingScriptReady()) {
     DCHECK(document_);
     DCHECK(!IsExecutingScript());
@@ -406,13 +414,17 @@ void HTMLParserScriptRunner::ExecuteParsingBlockingScripts() {
   }
 }
 
-void HTMLParserScriptRunner::ExecuteScriptsWaitingForLoad(
-    PendingScript* pending_script) {
+void HTMLParserScriptRunner::ExecuteScriptsWaitingForLoad() {
+  // Note(https://crbug.com/1093051): ExecuteScriptsWaitingForLoad() is
+  // triggered asynchronously from PendingScriptFinished(pending_script), but
+  // the |pending_script| might be no longer the ParserBlockginScript() here,
+  // because it might have been evaluated or disposed after
+  // PendingScriptFinished() before ExecuteScriptsWaitingForLoad(). Anyway we
+  // call ExecuteParsingBlockingScripts(), because necessary conditions for
+  // evaluation are checked safely there.
+
   TRACE_EVENT0("blink", "HTMLParserScriptRunner::executeScriptsWaitingForLoad");
   DCHECK(!IsExecutingScript());
-  DCHECK(HasParserBlockingScript());
-  DCHECK_EQ(pending_script, ParserBlockingScript());
-  DCHECK(ParserBlockingScript()->IsReady());
   ExecuteParsingBlockingScripts();
 }
 

third_party/blink/renderer/core/script/html_parser_script_runner.h

@@ -86,7 +86,7 @@ class HTMLParserScriptRunner final
 
   // Invoked when the parsing-blocking script resource has loaded, to execute
   // parsing-blocking scripts.
-  void ExecuteScriptsWaitingForLoad(PendingScript*);
+  void ExecuteScriptsWaitingForLoad();
 
   // Invoked when all script-blocking resources (e.g., stylesheets) have loaded,
   // to execute parsing-blocking scripts.

third_party/blink/renderer/core/script/html_parser_script_runner_host.h

@@ -32,14 +32,13 @@
 namespace blink {
 
 class HTMLInputStream;
-class PendingScript;
 
 class CORE_EXPORT HTMLParserScriptRunnerHost : public GarbageCollectedMixin {
  public:
   virtual ~HTMLParserScriptRunnerHost() = default;
   void Trace(Visitor* visitor) const override {}
 
-  virtual void NotifyScriptLoaded(PendingScript*) = 0;
+  virtual void NotifyScriptLoaded() = 0;
   virtual HTMLInputStream& InputStream() = 0;
 
   virtual bool HasPreloadScanner() const = 0;