[aw] Implement AwTracingDelegate::IsAllowedTo*BackgroundScenario()

This CL adds AwTracingDelegate overrides for IsAllowedToBeginBackgroundScenario()
and IsAllowedToEndBackgroundScenario() which return true to enable
background tracing for WebView.

Bug: b/170511349
Change-Id: I56e306ac37f6d4055b68bf54a5c009111ce31077
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2465873
Commit-Queue: Oksana Zhuravlova <oksamyt@chromium.org>
Reviewed-by: Michael Bai <michaelbai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817234}

android_webview/browser/tracing/aw_tracing_delegate.cc

@@ -23,6 +23,22 @@ std::unique_ptr<content::TraceUploader> AwTracingDelegate::GetTraceUploader(
   return NULL;
 }
 
+bool AwTracingDelegate::IsAllowedToBeginBackgroundScenario(
+    const content::BackgroundTracingConfig& config,
+    bool requires_anonymized_data) {
+  // Background tracing is allowed in general and can be restricted when
+  // configuring BackgroundTracingManager.
+  return true;
+}
+
+bool AwTracingDelegate::IsAllowedToEndBackgroundScenario(
+    const content::BackgroundTracingConfig& config,
+    bool requires_anonymized_data) {
+  // Background tracing is allowed in general and can be restricted when
+  // configuring BackgroundTracingManager.
+  return true;
+}
+
 std::unique_ptr<base::DictionaryValue>
 AwTracingDelegate::GenerateMetadataDict() {
   auto metadata_dict = std::make_unique<base::DictionaryValue>();

android_webview/browser/tracing/aw_tracing_delegate.h

@@ -23,6 +23,12 @@ class AwTracingDelegate : public content::TracingDelegate {
   // content::TracingDelegate implementation:
   std::unique_ptr<content::TraceUploader> GetTraceUploader(
       scoped_refptr<network::SharedURLLoaderFactory> factory) override;
+  bool IsAllowedToBeginBackgroundScenario(
+      const content::BackgroundTracingConfig& config,
+      bool requires_anonymized_data) override;
+  bool IsAllowedToEndBackgroundScenario(
+      const content::BackgroundTracingConfig& config,
+      bool requires_anonymized_data) override;
   std::unique_ptr<base::DictionaryValue> GenerateMetadataDict() override;
 };