Fix startup tracing to an arbitrary file Android

As a side effect of the tracing cleanups in https://crrev.com/c/1015647,
setting a custom startup trace file via --trace-startup-file stopped
working on Android. Fix by not hardcoding the call to generate a path,
so the switch is checked first.

Bug: 828993
Change-Id: Ifcfd0dc2ea41b09af0c409ba5d406eda5d920b8b
Reviewed-on: https://chromium-review.googlesource.com/1097326Reviewed-by: Ehsan Chiniforooshan <chiniforooshan@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Tomasz Śniatowski <tsniatowski@vewd.com>
Cr-Commit-Position: refs/heads/master@{#569012}

components/tracing/common/trace_startup_config.cc

@@ -161,11 +161,9 @@ int TraceStartupConfig::GetStartupDuration() const {
   return startup_duration_;
 }
 
-#if !defined(OS_ANDROID)
 base::FilePath TraceStartupConfig::GetResultFile() const {
   DCHECK(IsEnabled());
   return result_file_;
 }
-#endif
 
 }  // namespace tracing

components/tracing/common/trace_startup_config.h

@@ -43,15 +43,14 @@ namespace tracing {
 //                   the result file after shutting the browser down.
 //
 // result_file:      The file that contains the trace log. The default result
-//                   file path is chrometrace.log. Chrome will dump the trace
-//                   log to this file
+//                   file path is chrometrace.log, except on Android, where the
+//                   default path is generated by tracing controller. Chrome
+//                   will dump the trace log to this file
 //                   1) after startup_duration if it is specified;
 //                   2) or after browser shutdown if startup duration is 0.
 //                   One can also stop tracing and get the result by other ways,
 //                   e.g., by DevTools. In that case, the trace log will not be
 //                   saved to this file.
-//                   Notice: This is not supported on Android. The result file
-//                   path will be generated by tracing controller.
 //
 // The trace config file can be specified by the --trace-config-file flag on
 // most platforms except on Android, e.g., --trace-config-file=path/to/file/.
@@ -93,9 +92,7 @@ class TRACING_EXPORT TraceStartupConfig {
 
   base::trace_event::TraceConfig GetTraceConfig() const;
   int GetStartupDuration() const;
-#if !defined(OS_ANDROID)
   base::FilePath GetResultFile() const;
-#endif
 
  private:
   // This allows constructor and destructor to be private and usable only

content/browser/browser_main_loop.cc

@@ -1593,15 +1593,15 @@ void BrowserMainLoop::InitializeMojo() {
 base::FilePath BrowserMainLoop::GetStartupTraceFileName() const {
   base::FilePath trace_file;
 
-#if defined(OS_ANDROID)
-  TracingControllerAndroid::GenerateTracingFilePath(&trace_file);
-#else
   trace_file = tracing::TraceStartupConfig::GetInstance()->GetResultFile();
   if (trace_file.empty()) {
+#if defined(OS_ANDROID)
+    TracingControllerAndroid::GenerateTracingFilePath(&trace_file);
+#else
     // Default to saving the startup trace into the current dir.
     trace_file = base::FilePath().AppendASCII("chrometrace.log");
-  }
 #endif
+  }
 
   return trace_file;
 }