Background tracing: Fixed truncating of uploaded data

https://chromium-review.googlesource.com/c/chromium/src/+/1834576 broke
the legacy JSON upload of Slow Reports due to the data being truncated
as data() has different semantics between RefCountedString and std::string,
and the latter resulted in an unintended std::string constructor being
implicitly invoked and the data being treated as a null-terminated string.

R=ssid@chromium.org

Bug: 1014589
Change-Id: If4d11ceb86106cf9cbee89735692dc83c1f7c35e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1863855Reviewed-by: ssid <ssid@chromium.org>
Commit-Queue: oysteine <oysteine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706584}

chrome/browser/tracing/background_tracing_field_trial.cc

@@ -70,7 +70,7 @@ void BackgroundTracingUploadCallback(
       TraceEventMetadataSource::GetInstance()->GenerateLegacyMetadataDict();
 
   uploader->DoUpload(
-      file_contents->data(), content::TraceUploader::UNCOMPRESSED_UPLOAD,
+      *file_contents, content::TraceUploader::UNCOMPRESSED_UPLOAD,
       std::move(metadata), content::TraceUploader::UploadProgressCallback(),
       base::BindOnce(&OnBackgroundTracingUploadComplete, base::Owned(uploader),
                      std::move(callback)));

chrome/browser/tracing/navigation_tracing.cc

@@ -47,7 +47,7 @@ void NavigationUploadCallback(
       TraceEventMetadataSource::GetInstance()->GenerateLegacyMetadataDict();
 
   uploader->DoUpload(
-      file_contents->data(), content::TraceUploader::UNCOMPRESSED_UPLOAD,
+      *file_contents, content::TraceUploader::UNCOMPRESSED_UPLOAD,
       std::move(metadata), content::TraceUploader::UploadProgressCallback(),
       base::BindOnce(&OnNavigationTracingUploadComplete, base::Owned(uploader),
                      std::move(callback)));