Keep method from getting stripped by proguard.

The method is only used by test code.

TBR=tedchoc@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/777633004

Cr-Commit-Position: refs/heads/master@{#306707}

content/public/android/java/src/org/chromium/content/app/ContentApplication.java

@@ -9,6 +9,7 @@
 import android.os.MessageQueue;
 
 import org.chromium.base.BaseChromiumApplication;
+import org.chromium.base.VisibleForTesting;
 import org.chromium.base.library_loader.LibraryLoader;
 import org.chromium.content.browser.TracingControllerAndroid;
 
@@ -63,6 +64,7 @@ protected void initializeLibraryDependencies() {
      * @return Whether the library dependencies have been initialized and it is safe to issue
      *         requests to load the native library.
      */
+    @VisibleForTesting
     public boolean areLibraryDependenciesInitialized() {
         return mLibraryDependenciesInitialized;
     }