WebLayer: Add thread checks and docs for public callbacks.

Add UI thread checks for callbacks that are passed to the embedder.

Bug: none
Change-Id: I2cd643e406f056c112f1f77ab84e66ad8e96cd08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2326296
Commit-Queue: Evan Stade <estade@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792768}

weblayer/browser/java/org/chromium/weblayer_private/DownloadCallbackProxy.java

@@ -9,6 +9,7 @@ import android.content.pm.PackageManager;
 import android.os.RemoteException;
 import android.webkit.ValueCallback;
 
+import org.chromium.base.ThreadUtils;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
 import org.chromium.base.annotations.NativeMethods;
@@ -91,6 +92,7 @@ public final class DownloadCallbackProxy {
         ValueCallback<Boolean> callback = new ValueCallback<Boolean>() {
             @Override
             public void onReceiveValue(Boolean result) {
+                ThreadUtils.assertOnUiThread();
                 if (mNativeDownloadCallbackProxy == 0) {
                     throw new IllegalStateException("Called after destroy()");
                 }

weblayer/browser/java/org/chromium/weblayer_private/FullscreenCallbackProxy.java

@@ -7,6 +7,7 @@ package org.chromium.weblayer_private;
 import android.os.RemoteException;
 import android.webkit.ValueCallback;
 
+import org.chromium.base.ThreadUtils;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
 import org.chromium.base.annotations.NativeMethods;
@@ -46,6 +47,7 @@ public final class FullscreenCallbackProxy {
         ValueCallback<Void> exitFullscreenCallback = new ValueCallback<Void>() {
             @Override
             public void onReceiveValue(Void result) {
+                ThreadUtils.assertOnUiThread();
                 if (mNativeFullscreenCallbackProxy == 0) {
                     throw new IllegalStateException("Called after destroy()");
                 }

weblayer/browser/java/org/chromium/weblayer_private/MediaStreamManager.java

@@ -13,6 +13,7 @@ import android.util.AndroidRuntimeException;
 import android.webkit.ValueCallback;
 
 import org.chromium.base.ContextUtils;
+import org.chromium.base.ThreadUtils;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
 import org.chromium.base.annotations.NativeMethods;
@@ -178,6 +179,7 @@ public class MediaStreamManager {
                     audio, video, ObjectWrapper.wrap(new ValueCallback<Boolean>() {
                         @Override
                         public void onReceiveValue(Boolean allowed) {
+                            ThreadUtils.assertOnUiThread();
                             respondToStreamRequest(requestId, allowed.booleanValue());
                         }
                     }));

weblayer/public/java/org/chromium/weblayer/DownloadCallback.java

@@ -36,7 +36,8 @@ public abstract class DownloadCallback {
      * @param uri the target that is being downloaded
      * @param requestMethod the method (GET/POST etc...) of the download
      * @param requestInitiator the initiating Uri, if present
-     * @param callback a callback to allow or disallow the download. must be called to avoid leaks
+     * @param callback a callback to allow or disallow the download. Must be called to avoid leaks,
+     *         and must be called on the UI thread.
      *
      * @since 81
      */

weblayer/public/java/org/chromium/weblayer/FullscreenCallback.java

@@ -17,7 +17,7 @@ public abstract class FullscreenCallback {
      * running the supplied Runnable (calling exitFullscreenRunner.Run() results in calling
      * exitFullscreen()).
      *
-     * NOTE: the Runnable must not be used synchronously.
+     * NOTE: the Runnable must not be used synchronously, and must be run on the UI thread.
      */
     public abstract void onEnterFullscreen(@NonNull Runnable exitFullscreenRunner);
 

weblayer/public/java/org/chromium/weblayer/MediaCaptureCallback.java

@@ -25,8 +25,8 @@ public abstract class MediaCaptureCallback {
      *
      * @param audio if true, the new stream includes audio from a microphone.
      * @param video if true, the new stream includes video from a camera.
-     * @param requestResult a callback to be run with true if and when the stream
-     *     can start, or false if the stream should not start.
+     * @param requestResult a callback to be run with true if and when the stream can start, or
+     *         false if the stream should not start. Must be run on the UI thread.
      */
     public void onMediaCaptureRequested(
             boolean audio, boolean video, ValueCallback<Boolean> requestResult) {}