Move atrace enabling code from Chrome to WebView

android_webview/java/src/org/chromium/android_webview/AwBrowserProcess.java

Index: android_webview/java/src/org/chromium/android_webview/AwBrowserProcess.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwBrowserProcess.java b/android_webview/java/src/org/chromium/android_webview/AwBrowserProcess.java
index 6f6404aa5e21eb274bb758c0c8584b10ba71e73d..b3aa4f8a859b1ce420bf717d27fef4a4add8e98f 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwBrowserProcess.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwBrowserProcess.java
@@ -5,18 +5,25 @@
 package org.chromium.android_webview;
 
 import android.content.Context;
+import android.os.Build;
+import android.util.Log;
 
 import org.chromium.base.PathUtils;
 import org.chromium.base.ThreadUtils;
+import org.chromium.base.TraceEvent;
 import org.chromium.base.library_loader.LibraryLoader;
 import org.chromium.base.library_loader.ProcessInitException;
 import org.chromium.content.browser.BrowserStartupController;
 
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
 /**
  * Wrapper for the steps needed to initialize the java and native sides of webview chromium.
  */
 public abstract class AwBrowserProcess {
     private static final String PRIVATE_DATA_DIRECTORY_SUFFIX = "webview";
+    private static final String TAG = "AwBrowserProcess";
 
     /**
      * Loads the native library, and performs basic static construction of objects needed
@@ -27,11 +34,58 @@ public abstract class AwBrowserProcess {
         PathUtils.setPrivateDataDirectorySuffix(PRIVATE_DATA_DIRECTORY_SUFFIX);
         try {
             LibraryLoader.loadNow();
+            initTraceEvent();
         } catch (ProcessInitException e) {
             throw new RuntimeException("Cannot load WebView", e);
         }
     }
 
+    // TODO(benm): Move this function into WebView code in Android tree to avoid reflection.
+    private static void initTraceEvent() {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN) return;
+
+        try {
+            final Class<?> traceClass = Class.forName("android.os.Trace");
+            final long traceTagView = traceClass.getField("TRACE_TAG_WEBVIEW").getLong(null);
+
+            final Class<?> systemPropertiesClass = Class.forName("android.os.SystemProperties");
+            final Method systemPropertiesGetLongMethod = systemPropertiesClass.getDeclaredMethod(
+                    "getLong", String.class, Long.TYPE);
+            final Method addChangeCallbackMethod = systemPropertiesClass.getDeclaredMethod(
+                    "addChangeCallback", Runnable.class);
+
+            // Won't reach here if any of the above reflect lookups fail.
+            addChangeCallbackMethod.invoke(null, new Runnable() {
+                @Override
+                public void run() {
+                    try {
+                        long enabledFlags = (Long) systemPropertiesGetLongMethod.invoke(
+                                null, "debug.atrace.tags.enableflags", 0);
+                        TraceEvent.setATraceEnabled((enabledFlags & traceTagView) != 0);
+                    } catch (IllegalArgumentException e) {
+                        Log.e(TAG, "systemPropertyChanged", e);
+                    } catch (IllegalAccessException e) {
+                        Log.e(TAG, "systemPropertyChanged", e);
+                    } catch (InvocationTargetException e) {
+                        Log.e(TAG, "systemPropertyChanged", e);
+                    }
+                }
+            });
+        } catch (ClassNotFoundException e) {
+            Log.e(TAG, "initTraceEvent", e);
+        } catch (NoSuchMethodException e) {
+            Log.e(TAG, "initTraceEvent", e);
+        } catch (IllegalArgumentException e) {
+            Log.e(TAG, "initTraceEvent", e);
+        } catch (IllegalAccessException e) {
+            Log.e(TAG, "initTraceEvent", e);
+        } catch (InvocationTargetException e) {
+            Log.e(TAG, "initTraceEvent", e);
+        } catch (NoSuchFieldException e) {
+            Log.e(TAG, "initTraceEvent", e);
+        }
+    }
+
     /**
      * Starts the chromium browser process running within this process. Creates threads
      * and performs other per-app resource allocations; must not be called from zygote.