Reland of Android: Add support for TraceEvent before the native library is loaded.

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 878275c2b80a60b28a8b763a53cdc5441d3c0a83..95d01dcef21e26d75c3c8d57c0d25eb7ed56e0ff 100644
--- a/base/android/java/src/org/chromium/base/TraceEvent.java
+++ b/base/android/java/src/org/chromium/base/TraceEvent.java
@@ -16,8 +16,8 @@ import org.chromium.base.annotations.JNINamespace;
  * Java mirror of Chrome trace event API. See base/trace_event/trace_event.h. Unlike the native
  * version, Java does not have stack objects, so a TRACE_EVENT() which does both TRACE_EVENT_BEGIN()
  * and TRACE_EVENT_END() in ctor/dtor is not possible.
- * It is OK to use tracing before the native library has loaded, but such traces will
- * be ignored. (Perhaps we could devise to buffer them up in future?).
+ * It is OK to use tracing before the native library has loaded, in a slightly restricted fashion.
+ * @see EarlyTraceEvent for details.
  */
 @JNINamespace("base::android")
 public class TraceEvent {
@@ -179,6 +179,7 @@ public class TraceEvent {
      */
     @CalledByNative
     public static void setEnabled(boolean enabled) {
+        if (enabled) EarlyTraceEvent.disable();
         sEnabled = enabled;
         // Android M+ systrace logs this on its own. Only log it if not writing to Android systrace.
         if (sATraceEnabled) return;
@@ -187,6 +188,15 @@ public class TraceEvent {
     }
 
     /**
+     * May enable early tracing depending on the environment.
+     *
+     * Must be called after the command-line has been read.
+     */
+    public static void maybeEnableEarlyTracing() {
+        EarlyTraceEvent.maybeEnable();
+    }
+
+    /**
      * Enables or disabled Android systrace path of Chrome tracing. If enabled, all Chrome
      * traces will be also output to Android systrace. Because of the overhead of Android
      * systrace, this is for WebView only.
@@ -254,7 +264,7 @@ public class TraceEvent {
      * @param name The name of the event.
      */
     public static void begin(String name) {
-        if (sEnabled) nativeBegin(name, null);
+        begin(name, null);
     }
 
     /**
@@ -263,6 +273,7 @@ public class TraceEvent {
      * @param arg  The arguments of the event.
      */
     public static void begin(String name, String arg) {
+        EarlyTraceEvent.begin(name);
         if (sEnabled) nativeBegin(name, arg);
     }
 
@@ -271,7 +282,7 @@ public class TraceEvent {
      * @param name The name of the event.
      */
     public static void end(String name) {
-        if (sEnabled) nativeEnd(name, null);
+        end(name, null);
     }
 
     /**
@@ -280,6 +291,7 @@ public class TraceEvent {
      * @param arg  The arguments of the event.
      */
     public static void end(String name, String arg) {
+        EarlyTraceEvent.end(name);
         if (sEnabled) nativeEnd(name, arg);
     }