Removed unnecessary potential locking

Function isInitialized, unlike calls ensureinitialized should not block
the thread, but it will if initialization is in progress at this moment.
It is not necessery to synchronize the sInitialized flag in
isInitialized function. It is enough that flag have a primitive type and
has a volatile qualifier.

R=nyquist@chromium.org, rmcilroy@chromium.org
TEST=It is rather hard to test. We've found ~300ms stuck on UI thread,
on calling LibraryLoader.isInitialized from ContentApplication.onCreate
with profiler

Review URL: https://codereview.chromium.org/925513002

Cr-Commit-Position: refs/heads/master@{#318208}

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

@@ -42,7 +42,7 @@ public class LibraryLoader {
     private static final Object sLock = new Object();
 
     // The singleton instance of LibraryLoader.
-    private static LibraryLoader sInstance;
+    private static volatile LibraryLoader sInstance;
 
     // One-way switch becomes true when the libraries are loaded.
     private boolean mLoaded;
@@ -54,7 +54,9 @@ public class LibraryLoader {
     // One-way switch becomes true when the libraries are initialized (
     // by calling nativeLibraryLoaded, which forwards to LibraryLoaded(...) in
     // library_loader_hooks.cc).
-    private boolean mInitialized;
+    // Note that this member should remain a one-way switch, since it accessed from multiple
+    // threads without a lock.
+    private volatile boolean mInitialized;
 
     // One-way switches recording attempts to use Relro sharing in the browser.
     // The flags are used to report UMA stats later.
@@ -81,7 +83,9 @@ public class LibraryLoader {
     private boolean mLibraryIsMappableInApk = true;
 
     // The type of process the shared library is loaded in.
-    private int mLibraryProcessType;
+    // This member can be accessed from multiple threads simultaneously, so it have to be
+    // final (like now) or be protected in some way (volatile of synchronized).
+    private final int mLibraryProcessType;
 
     /**
      * @param libraryProcessType the process the shared library is loaded in. refer to
@@ -141,9 +145,7 @@ public class LibraryLoader {
      * Checks if library is fully loaded and initialized.
      */
     public static boolean isInitialized() {
-        synchronized (sLock) {
-            return sInstance != null && sInstance.mInitialized;
-        }
+        return sInstance != null && sInstance.mInitialized;
     }
 
     /**
@@ -377,10 +379,6 @@ public class LibraryLoader {
             Log.e(TAG, "error calling nativeLibraryLoaded");
             throw new ProcessInitException(LoaderErrors.LOADER_ERROR_FAILED_TO_REGISTER_JNI);
         }
-        // From this point on, native code is ready to use and checkIsReady()
-        // shouldn't complain from now on (and in fact, it's used by the
-        // following calls).
-        mInitialized = true;
 
         // The Chrome JNI is registered by now so we can switch the Java
         // command line over to delegating to native if it's necessary.
@@ -391,6 +389,13 @@ public class LibraryLoader {
 
         // From now on, keep tracing in sync with native.
         TraceEvent.registerNativeEnabledObserver();
+
+        // From this point on, native code is ready to use and checkIsReady()
+        // shouldn't complain from now on (and in fact, it's used by the
+        // following calls).
+        // Note that this flag can be accessed asynchronously, so any initialization
+        // must be performed before.
+        mInitialized = true;
     }
 
     // Called after all native initializations are complete.
@@ -455,10 +460,8 @@ public class LibraryLoader {
      */
     @CalledByNative
     public static int getLibraryProcessType() {
-        synchronized (sLock) {
-            if (sInstance == null) return LibraryProcessType.PROCESS_UNINITIALIZED;
-            return sInstance.mLibraryProcessType;
-        }
+        if (sInstance == null) return LibraryProcessType.PROCESS_UNINITIALIZED;
+        return sInstance.mLibraryProcessType;
     }
 
     private native void nativeInitCommandLine(String[] initCommandLine);