Remove usages of namespace in generate_jni in BUILD.gn files

This CL removes usages of namespace in generate_jni, and use
@JNINamespace("foo") instead.

Bug: 396707350
Change-Id: Ia6d76760a22cf00cb42037ec4761a35b4c2fec36
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7363020
Owners-Override: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Martin Kong <martinkong@google.com>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1567791}
NOKEYCHECK=True
GitOrigin-RevId: 45a5f753d943301d61a73c3f69d9e16f206f2f3e

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index a568d28..b7b391c 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -40,7 +40,6 @@
 
 if (!is_cronet_build && is_android) {
   generate_jni("jni_headers") {
-    namespace = "metrics"
     sources = [
       "android/java/src/org/chromium/components/metrics/LowEntropySource.java",
     ]

android/java/src/org/chromium/components/metrics/LowEntropySource.java

diff --git a/android/java/src/org/chromium/components/metrics/LowEntropySource.java b/android/java/src/org/chromium/components/metrics/LowEntropySource.java
index e1c76c8..12405d8 100644
--- a/android/java/src/org/chromium/components/metrics/LowEntropySource.java
+++ b/android/java/src/org/chromium/components/metrics/LowEntropySource.java
@@ -9,6 +9,7 @@
 import androidx.annotation.MainThread;
 
 import org.jni_zero.CalledByNative;
+import org.jni_zero.JNINamespace;
 
 import org.chromium.base.ContextUtils;
 import org.chromium.base.ThreadUtils;
@@ -18,12 +19,13 @@
 
 /**
  * Generates a new non-identifying entropy source used to seed persistent activities. Has a static
- * cache so that the new low entropy source value will only be generated on first access.
- * Low entropy source is queried by entropy_source.cc that caches it in prefs. On Android, it is
+ * cache so that the new low entropy source value will only be generated on first access. Low
+ * entropy source is queried by entropy_source.cc that caches it in prefs. On Android, it is
  * generated in Java so that it can be used by FRE experiments when the native is not available yet.
  */
 @MainThread
 @NullMarked
+@JNINamespace("metrics")
 public class LowEntropySource {
     // Should be equal to the value of EntropyState::kMaxLowEntropySize in C++.
     public static final int MAX_LOW_ENTROPY_SIZE = 8000;