Roll buildroot to support Android SDK 28 (#7245)

* Roll to buildroot and support Android SDK 28

* Ubuntu 16 for android build test

DEPS

@@ -117,7 +117,7 @@ allowed_hosts = [
 ]
 
 deps = {
-  'src': 'https://github.com/flutter/buildroot.git' + '@' + '8e538639660413490ea9261eee84864005e240f4',
+  'src': 'https://github.com/flutter/buildroot.git' + '@' + '5f54a3e98dea0a79589820527658b49fef7916ea',
 
    # Fuchsia compatibility
    #

ci/docker/build/Dockerfile

-FROM ubuntu:14.04
+FROM ubuntu:16.04
 
 ENV DEPOT_TOOLS_PATH $HOME/depot_tools
 ENV ENGINE_PATH $HOME/engine

shell/platform/android/BUILD.gn

@@ -146,16 +146,16 @@ java_library("flutter_shell_java") {
   ]
 
   deps = [
-    ":android_support_v4",
+    ":android_support_v13",
   ]
 
   jar_path = "$root_out_dir/flutter_java.jar"
 }
 
-java_prebuilt("android_support_v4") {
+java_prebuilt("android_support_v13") {
   supports_android = true
 
-  jar_path = "//third_party/android_tools/sdk/extras/android/support/v4/android-support-v4.jar"
+  jar_path = "//third_party/android_tools/sdk/extras/android/support/v13/android-support-v13.jar"
 }
 
 copy("flutter_shell_assets") {