Disable image prefetch for Android.

Android requires a different mechanism to prefetch suggestion images
to avoid copying byte buffers from C++ to Java and replicating caches.

Bug: 930349
Change-Id: I243ccb7c6832f0b9333ffb72a31b0d770a643c8e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1600963Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Ender <ender@google.com>
Cr-Commit-Position: refs/heads/master@{#663878}

chrome/browser/autocomplete/chrome_autocomplete_provider_client.cc

@@ -313,6 +313,9 @@ void ChromeAutocompleteProviderClient::DeleteMatchingURLsForKeywordFromHistory(
 }
 
 void ChromeAutocompleteProviderClient::PrefetchImage(const GURL& url) {
+  // Note: Android uses different image fetching mechanism to avoid
+  // penalty of copying byte buffers from C++ to Java.
+#if !defined(OS_ANDROID)
   BitmapFetcherService* image_service =
       BitmapFetcherServiceFactory::GetForBrowserContext(profile_);
   DCHECK(image_service);
@@ -358,6 +361,7 @@ void ChromeAutocompleteProviderClient::PrefetchImage(const GURL& url) {
         })");
 
   image_service->Prefetch(url, traffic_annotation);
+#endif  // !defined(OS_ANDROID)
 }
 
 void ChromeAutocompleteProviderClient::StartServiceWorker(