Prefetch the native library from native code by parsing /proc/pid/maps.

base/android/java/src/org/chromium/base/library_loader/LibraryLoader.java

Index: base/android/java/src/org/chromium/base/library_loader/LibraryLoader.java
diff --git a/base/android/java/src/org/chromium/base/library_loader/LibraryLoader.java b/base/android/java/src/org/chromium/base/library_loader/LibraryLoader.java
index 484c6bc56d55596cdf77610e3cbf8e541c4d3d67..67e95144b1bda11dba8dd1ce92985c8b2a00b096 100644
--- a/base/android/java/src/org/chromium/base/library_loader/LibraryLoader.java
+++ b/base/android/java/src/org/chromium/base/library_loader/LibraryLoader.java
@@ -250,15 +250,23 @@ public class LibraryLoader {
         new AsyncTask<Void, Void, Void>() {
             @Override
             protected Void doInBackground(Void... params) {
-                // Note: AsyncTasks are executed in a low priority background
-                // thread, which is the desired behavior here since we don't
-                // want to interfere with the rest of the initialization.
-                for (String library : NativeLibraries.LIBRARIES) {
-                    if (Linker.isChromiumLinkerLibrary(library)) {
-                        continue;
+                TraceEvent.begin("LibraryLoader.asyncPrefetchLibrariesToMemory");
+                // First, try to fork a new process to do the prefetch. If it
+                // fails, fall back to doing it by mapping the library.
+                boolean ok = nativeForkAndPrefetchNativeLibrary();
+                if (!ok) {
+                    Log.w(TAG, "Forking a process to prefetch the native library failed.");
+                    // Note: AsyncTasks are executed in a low priority background

[pasko, 2015/03/27 11:03:37]

s/Note: //

[Benoit L, 2015/03/27 15:44:51]

Done.

+                    // thread, which is the desired behavior here since we don't

[pasko, 2015/03/27 11:03:37]

Please avoid using 'we' in comments, writing in third person is always
preferable.

[Benoit L, 2015/03/27 15:44:51]

Done.

+                    // want to interfere with the rest of the initialization.
+                    for (String library : NativeLibraries.LIBRARIES) {
+                        if (Linker.isChromiumLinkerLibrary(library)) {
+                            continue;
+                        }
+                        prefetchLibraryToMemory(context, library);
                     }
-                    prefetchLibraryToMemory(context, library);
                 }
+                TraceEvent.end("LibraryLoader.asyncPrefetchLibrariesToMemory");
                 return null;
             }
         }.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
@@ -573,4 +581,9 @@ public class LibraryLoader {
     // Get the version of the native library. This is needed so that we can check we
     // have the right version before initializing the (rest of the) JNI.
     private native String nativeGetVersionNumber();
+
+    // Finds the ranges corresponding to the native library pages, forks a new
+    // process to prefetch these pages and waits for it. The new process then
+    // terminates. This is blocking.
+    private static native boolean nativeForkAndPrefetchNativeLibrary();
 }