Remove the proguard keep rule for AwDebug now @UsedByReflection works.

BUG=541543

Review-Url: https://codereview.chromium.org/2364733004
Cr-Commit-Position: refs/heads/master@{#420612}

android_webview/apk/java/proguard.flags

@@ -50,11 +50,6 @@
 }
 -dontnote com.android.webview.chromium.PlatformServiceBridgeGoogle
 
-# AwDebug is accessed by reflection.
--keep class org.chromium.android_webview.AwDebug {
-  public static boolean dumpWithoutCrashing(...);
-}
-
 #TODO(hush): remove after N release. crbug.com/546762
 -keep class com.android.webview.chromium.ContentSettingsAdapter {
   public void setDisabledActionModeMenuItems(int);

android_webview/java/src/org/chromium/android_webview/AwDebug.java

@@ -5,6 +5,7 @@
 package org.chromium.android_webview;
 
 import org.chromium.base.annotations.JNINamespace;
+import org.chromium.base.annotations.UsedByReflection;
 
 import java.io.File;
 import java.io.IOException;
@@ -16,6 +17,7 @@ import java.io.IOException;
  * the client of WebView.
  */
 @JNINamespace("android_webview")
+@UsedByReflection("")
 public class AwDebug {
     /**
      * Dump webview state (predominantly a minidump for all threads,
@@ -29,6 +31,7 @@ public class AwDebug {
      * be able to be re-opened for reading and writing via its
      * canonical path. The file will be truncated upon re-opening.
      */
+    @UsedByReflection("")
     public static boolean dumpWithoutCrashing(File dumpFile) {
         String dumpPath;
         try {