android: Record early toplevel Looper events in tracing.

base/android/java/src/org/chromium/base/TraceEvent.java

Index: base/android/java/src/org/chromium/base/TraceEvent.java
diff --git a/base/android/java/src/org/chromium/base/TraceEvent.java b/base/android/java/src/org/chromium/base/TraceEvent.java
index b2f978244b16f61083be1c6a5feecb9b5a71f502..f30cbdba3264c5883fbd2c3a6132db11e0ddc8ea 100644
--- a/base/android/java/src/org/chromium/base/TraceEvent.java
+++ b/base/android/java/src/org/chromium/base/TraceEvent.java
@@ -27,6 +27,8 @@ public class TraceEvent {
     private static volatile boolean sATraceEnabled; // True when taking an Android systrace.
 
     private static class BasicLooperMonitor implements Printer {
+        private static final String EARLY_TOPLEVEL_TASK_NAME = "Looper.dispatchMessage: ";
+
         @Override
         public void println(final String line) {
             if (line.startsWith(">")) {
@@ -38,19 +40,37 @@ public class TraceEvent {
         }
 
         void beginHandling(final String line) {
-            if (sEnabled) {
-                // Android Looper formats |line| as ">>>>> Dispatching to (TARGET) [...]" since at
-                // least 2009 (Donut). Extracts the TARGET part of the message.
-                int start = line.indexOf('(', 21); // strlen(">>>>> Dispatching to ")
-                int end = start == -1 ? -1 : line.indexOf(')', start);
-                String target = end != -1 ? line.substring(start + 1, end) : "";
-                nativeBeginToplevel(target);
+            // May return an out-of-date value. this is not an issue as EarlyTraceEvent#begin()
+            // will filter the event in this case.
+            boolean earlyTracingActive = EarlyTraceEvent.isActive();
+            if (sEnabled || earlyTracingActive) {
+                String target = getTarget(line);
+                if (sEnabled) {
+                    nativeBeginToplevel(target);
+                } else if (earlyTracingActive) {
+                    // Synthesize a task name instead of using a parameter, as early tracing doesn't
+                    // support parameters.
+                    EarlyTraceEvent.begin(EARLY_TOPLEVEL_TASK_NAME + target);
+                }
             }
         }
 
         void endHandling(final String line) {
+            if (EarlyTraceEvent.isActive()) {
+                EarlyTraceEvent.end(EARLY_TOPLEVEL_TASK_NAME + getTarget(line));
+            }
             if (sEnabled) nativeEndToplevel();
         }
+
+        /**
+         * Android Looper formats |line| as ">>>>> Dispatching to (TARGET) [...]" since at least
+         * 2009 (Donut). Extracts the TARGET part of the message.
+         */
+        private static String getTarget(String logLine) {
+            int start = logLine.indexOf('(', 21); // strlen(">>>>> Dispatching to ")
+            int end = start == -1 ? -1 : logLine.indexOf(')', start);
+            return end != -1 ? logLine.substring(start + 1, end) : "";
+        }
     }
 
     /**
@@ -207,6 +227,9 @@ public class TraceEvent {
      */
     public static void maybeEnableEarlyTracing() {
         EarlyTraceEvent.maybeEnable();
+        if (EarlyTraceEvent.isActive()) {
+            ThreadUtils.getUiThreadLooper().setMessageLogging(LooperMonitorHolder.sInstance);
+        }
     }
 
     /**