Add proguard definitions to prevent stripping of methods

android_webview/apk/java/proguard.flags

 # Don't rename anything, it makes stack traces unintelligible. We only allow the
 # obfuscation pass to run so that we can discard attributes like local variable
 # tables.
 -keepnames class *** { *; }
 
 # Keep source file and line number information for stack traces.
 -keepattributes SourceFile,LineNumberTable
 
 # Keep all runtime visible annotations.
 -keepattributes RuntimeVisibleAnnotations
@@ skipping 67 matching lines @@
 -keep class com.android.webview.chromium.WebViewChromium {
   public void extractSmartClipData(int,int,int,int);
   public void setSmartClipResultHandler(android.os.Handler);
 }
 
 # AwDebug is accessed by reflection.
 -keep class org.chromium.android_webview.AwDebug {
   public static boolean dumpWithoutCrashing(...);
 }
 
-#TODO(hush): remove after N release. crbug.com/543272, crbug.com/584789
+#TODO(hush): remove after N release. crbug.com/543272, crbug.com/584789.
+#TODO(hush): Also remove getHandler and findFocus when removing others here
+#            and add @Override to these methods.
 -keep class com.android.webview.chromium.WebViewChromium {
   public void onActivityResult(int,int,android.content.Intent);
   public boolean onDragEvent(android.view.DragEvent);
+  public android.os.Handler getHandler(android.os.Handler);
+  public android.view.View findFocus(android.view.View);
 }
 
 #TODO(hush): remove after N release. crbug.com/546762
 -keep class com.android.webview.chromium.ContentSettingsAdapter {
   public void setDisabledActionModeMenuItems(int);
   public int getDisabledActionModeMenuItems();
 }
 
 # Ignore notes and warnings about the support library, which uses reflection and
 # may reference classes no longer in the SDK.
 -dontnote android.support.**
 -dontwarn android.support.**
 
 # Keep all enum values and valueOf methods. See
 # http://proguard.sourceforge.net/index.html#manual/examples.html
 # for the reason for this. Also, see http://crbug.com/248037.
 -keepclassmembers enum * {
     public static **[] values();
     public static ** valueOf(java.lang.String);
 }