Default active resource retention false.

Although Glide avoids recycling or mutating Bitmaps recovered from
active resources via weak references, we can't prevent callers from
doing so. If callers do mutate or recycle the Bitmaps, Glide may throw
exceptions, show graphical errors, or experience other undefined
behavior. Since we can't guarantee that Glide's behavior is safe, it
doesn't make sense to default this option on.

That said, recycling or mutating Bitmaps returned by Glide isn't
strictly safe either and is generally both bad and inefficient. If
applications use the safe and efficient RequestManager.clear method
instead, setting this option to true will work as expected. As a result,
we'll retain the option, but force users to opt in if they want the
benefit.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=178704468

library/src/main/java/com/bumptech/glide/GlideBuilder.java

@@ -1,6 +1,7 @@
 package com.bumptech.glide;
 
 import android.content.Context;
+import android.graphics.Bitmap;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v4.util.ArrayMap;
@@ -23,6 +24,7 @@
 import com.bumptech.glide.manager.RequestManagerRetriever;
 import com.bumptech.glide.manager.RequestManagerRetriever.RequestManagerFactory;
 import com.bumptech.glide.request.RequestOptions;
+import com.bumptech.glide.request.target.Target;
 import java.util.Map;
 
 /**
@@ -46,7 +48,7 @@ public final class GlideBuilder {
   @Nullable
   private RequestManagerFactory requestManagerFactory;
   private GlideExecutor animationExecutor;
-  private boolean isActiveResourceRetentionAllowed = true;
+  private boolean isActiveResourceRetentionAllowed;
 
   /**
    * Sets the {@link com.bumptech.glide.load.engine.bitmap_recycle.BitmapPool} implementation to use
@@ -345,6 +347,8 @@ public GlideBuilder setLogLevel(int logLevel) {
    * {@link com.bumptech.glide.request.target.Target}s which are subsequently de-referenced and
    * garbage collected without being cleared.
    *
+   * <p>Defaults to {@code false}.
+   *
    * <p>Glide's resource re-use system is permissive, which means that's acceptable for callers to
    * load resources into {@link com.bumptech.glide.request.target.Target}s and then never clear the
    * {@link com.bumptech.glide.request.target.Target}. To do so, Glide uses
@@ -359,17 +363,25 @@ public GlideBuilder setLogLevel(int logLevel) {
    * setting this method to {@code true} may transiently increase the memory usage of an
    * application.
    *
-   * <p>Setting this method to {@code false} will allow the platform to garbage collect resources
-   * more quickly, but will lead to unexpected memory cache misses if callers load resources into
-   * {@link com.bumptech.glide.request.target.Target}s but never clear them.
+   * <p>Leaving this method at the default {@code false} value will allow the platform to garbage
+   * collect resources more quickly, but will lead to unexpected memory cache misses if callers load
+   * resources into {@link com.bumptech.glide.request.target.Target}s but never clear them.
+   *
+   * <p>If you set this method to {@code true} you <em>must not</em> call
+   * {@link Bitmap#recycle()} or mutate any Bitmaps returned by Glide. If this method is set to
+   * {@code false}, recycling or mutating Bitmaps is inefficient but safe as long as you do not
+   * clear the corresponding {@link com.bumptech.glide.request.target.Target} used to load the
+   * {@link Bitmap}. However, if you set this method to {@code true} and recycle or mutate any
+   * returned {@link Bitmap}s or other mutable resources, Glide may recover those resources and
+   * attempt to use them later on, resulting in crashes, graphical corruption or undefined behavior.
    *
    * <p>Regardless of what value this method is set to, it's always good practice to clear
    * {@link com.bumptech.glide.request.target.Target}s when you're done with the corresponding
    * resource. Clearing {@link com.bumptech.glide.request.target.Target}s allows Glide to maximize
    * resource re-use, minimize memory overhead and minimize unexpected behavior resulting from
-   * edge cases.
-   *
-   * <p>Defaults to {@code true}.
+   * edge cases. If you use {@link RequestManager#clear(Target)}, calling {@link Bitmap#recycle()}
+   * or mutating {@link Bitmap}s is not only unsafe, it's also totally unnecessary and should be
+   * avoided. In all cases, prefer {@link RequestManager#clear(Target)} to {@link Bitmap#recycle()}.
    *
    * @return This builder.
    */