Revert "Remove default startAllowlistLookup interface"

This reverts commit e0b95885.

Reason for revert: this broke downstream WebView compile (https://crbug.com/1012531)

Original change's description:
> Remove default startAllowlistLookup interface
> 
> Bug: 995926
> Change-Id: I76ac44526fcf7241b800899810db81dbdd598ae3
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1846092
> Reviewed-by: Varun Khaneja <vakh@chromium.org>
> Commit-Queue: Xinghui Lu <xinghuilu@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#703911}

TBR=vakh@chromium.org,xinghuilu@chromium.org

Change-Id: I282a1a33cd92a79930d1b35e3fa42022472fa171
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 995926, 1012531
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1848349Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703971}

components/safe_browsing/android/java/src/org/chromium/components/safe_browsing/SafeBrowsingApiHandler.java

@@ -82,5 +82,8 @@ public interface SafeBrowsingApiHandler {
      *
      * @return true if the uri is found in the corresponding allowlist. Otherwise, false.
      */
-    public boolean startAllowlistLookup(String uri, int threatType);
+    // TODO(xinghuilu@): remove default once downstream implementation is patched
+    default boolean startAllowlistLookup(String uri, int threatType) {
+        return false;
+    }
 }