Use a temporary trace file to avoid corrupt traces

R=gab@chromium.org,eseckler@chromium.org

Bug: 1082916
Change-Id: Ie0f50d29df84b360ecc7a556bcbaea5801b73f32
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225245
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774680}

content/browser/tracing/tracing_controller_impl_data_endpoint.cc

@@ -85,11 +85,14 @@ class FileTraceDataEndpoint : public TracingController::TraceDataEndpoint {
   }
 
   bool OpenFileIfNeededOnBlockingThread() {
-    base::ScopedBlockingCall scoped_blocking_call(
-        FROM_HERE, base::BlockingType::MAY_BLOCK);
     if (file_ != nullptr)
       return true;
-    file_ = base::OpenFile(file_path_, "w");
+
+    // The temporary trace file is produced in the same folder since paths must
+    // be on the same volume.
+    file_ = FileToFILE(CreateAndOpenTemporaryFileInDir(file_path_.DirName(),
+                                                       &pending_file_path_),
+                       "w");
     if (file_ == nullptr) {
       LOG(ERROR) << "Failed to open " << file_path_.value();
       return false;
@@ -103,6 +106,14 @@ class FileTraceDataEndpoint : public TracingController::TraceDataEndpoint {
       file_ = nullptr;
     }
 
+    base::File::Error error;
+    if (!base::ReplaceFile(pending_file_path_, file_path_, &error)) {
+      LOG(ERROR) << "Cannot replace file '" << file_path_
+                 << "' : " << base::File::ErrorToString(error);
+      base::DeleteFile(pending_file_path_, false);
+      return;
+    }
+
     GetUIThreadTaskRunner({})->PostTask(
         FROM_HERE,
         base::BindOnce(&FileTraceDataEndpoint::FinalizeOnUIThread, this));
@@ -111,6 +122,7 @@ class FileTraceDataEndpoint : public TracingController::TraceDataEndpoint {
   void FinalizeOnUIThread() { std::move(completion_callback_).Run(); }
 
   base::FilePath file_path_;
+  base::FilePath pending_file_path_;
   base::OnceClosure completion_callback_;
   FILE* file_ = nullptr;
   const scoped_refptr<base::SequencedTaskRunner> may_block_task_runner_;