Switch to a java exception in assertOnUiThread.

base/android/java/src/org/chromium/base/ThreadUtils.java

Index: base/android/java/src/org/chromium/base/ThreadUtils.java
diff --git a/base/android/java/src/org/chromium/base/ThreadUtils.java b/base/android/java/src/org/chromium/base/ThreadUtils.java
index ef2887acd0c97e5c8ca97beb489c1dbe50302d98..5fc1d21324abc6155488a31736d1739faf5e17b8 100644
--- a/base/android/java/src/org/chromium/base/ThreadUtils.java
+++ b/base/android/java/src/org/chromium/base/ThreadUtils.java
@@ -189,7 +189,9 @@ public class ThreadUtils {
      * Asserts that the current thread is running on the main thread.
      */
     public static void assertOnUiThread() {
-        assert runningOnUiThread();
+        if (BuildConfig.IS_DEBUG && !runningOnUiThread()) {
+            throw new IllegalStateException("Must be called on the Ui thread.");
+        }
     }
 
     /**