[tracing] Clean up trace name generation on Android.

Make generateTracingFilePath take a basename as a parameter, to allow
C++ to customise the file name while relying on Java to figure out the
correct directory.

If an empty string is passed, Java will generate an appropriate unique
name.

R=skyostil@chromium.org
BUG=1157954

Change-Id: Ie94448ef1db1f57d0f15deba5fa54753285ea429
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2588331
Commit-Queue: Alexander Timin <altimin@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839973}

content/browser/android/tracing_controller_android.cc

@@ -161,12 +161,13 @@ void TracingControllerAndroid::StopTracing(
   session->data->Stop();
 }
 
-void TracingControllerAndroid::GenerateTracingFilePath(
-    base::FilePath* file_path) {
+base::FilePath TracingControllerAndroid::GenerateTracingFilePath(
+    const std::string& basename) {
   JNIEnv* env = base::android::AttachCurrentThread();
   ScopedJavaLocalRef<jstring> jfilename =
-      Java_TracingControllerAndroidImpl_generateTracingFilePath(env);
-  *file_path = base::FilePath(
+      Java_TracingControllerAndroidImpl_generateTracingFilePath(
+          env, base::android::ConvertUTF8ToJavaString(env, basename));
+  return base::FilePath(
       base::android::ConvertJavaStringToUTF8(env, jfilename.obj()));
 }
 

content/browser/android/tracing_controller_android.h

@@ -39,7 +39,11 @@ class TracingControllerAndroid {
       JNIEnv* env,
       const base::android::JavaParamRef<jobject>& obj,
       const base::android::JavaParamRef<jobject>& callback);
-  static void GenerateTracingFilePath(base::FilePath* file_path);
+
+  // Locate the appropriate directory to write the trace to and use it to
+  // generate the path. |basename| might be empty, then TracingControllerAndroid
+  // will generate an appropriate one as well.
+  static base::FilePath GenerateTracingFilePath(const std::string& basename);
 
  private:
   ~TracingControllerAndroid();

content/browser/tracing/startup_tracing_controller.cc

@@ -213,7 +213,7 @@ base::FilePath GetStartupTraceFileName() {
   trace_file = tracing::TraceStartupConfig::GetInstance()->GetResultFile();
   if (trace_file.empty()) {
 #if defined(OS_ANDROID)
-    TracingControllerAndroid::GenerateTracingFilePath(&trace_file);
+    trace_file = TracingControllerAndroid::GenerateTracingFilePath("");
 #else
     // Default to saving the startup trace into the current dir.
     trace_file = base::FilePath().AppendASCII("chrometrace.log");

content/public/android/java/src/org/chromium/content/browser/TracingControllerAndroidImpl.java

@@ -122,23 +122,28 @@ public class TracingControllerAndroidImpl implements TracingControllerAndroid {
     }
 
     /**
-     * Generates a unique filename to be used for tracing in the Downloads directory.
+     * Generates a filepath to be used for tracing in the Downloads directory.
+     * @param basename The basename to be used, if empty a unique one will be generated.
      */
     @CalledByNative
-    private static String generateTracingFilePath() {
+    private static String generateTracingFilePath(String basename) {
         try (StrictModeContext ignored = StrictModeContext.allowDiskWrites()) {
             String state = Environment.getExternalStorageState();
             if (!Environment.MEDIA_MOUNTED.equals(state)) {
                 return null;
             }
 
-            // Generate a hopefully-unique filename using the UTC timestamp.
-            // (Not a huge problem if it isn't unique, we'll just append more data.)
-            SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd-HHmmss", Locale.US);
-            formatter.setTimeZone(TimeZone.getTimeZone("UTC"));
+            if (basename.isEmpty()) {
+                // Generate a hopefully-unique filename using the UTC timestamp.
+                // (Not a huge problem if it isn't unique, we'll just append more data.)
+                SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd-HHmmss", Locale.US);
+                formatter.setTimeZone(TimeZone.getTimeZone("UTC"));
+                basename = "chrome-profile-results-" + formatter.format(new Date());
+            }
+
             Context context = ContextUtils.getApplicationContext();
             File dir = context.getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS);
-            File file = new File(dir, "chrome-profile-results-" + formatter.format(new Date()));
+            File file = new File(dir, basename);
             return file.getPath();
         }
     }
@@ -169,7 +174,7 @@ public class TracingControllerAndroidImpl implements TracingControllerAndroid {
         mShowToasts = showToasts;
 
         if (filename == null) {
-            filename = generateTracingFilePath();
+            filename = generateTracingFilePath("");
             if (filename == null) {
                 logAndToastError(mContext.getString(R.string.profiler_no_storage_toast));
                 return false;