Cherry-pick: aw: Use async upload by default

Clean cherry-pick of chromium crrev.com/r289252

BUG: 16550863
Change-Id: I48eaa5843313b918f001242f073c762de43e5819
diff --git a/android_webview/lib/main/aw_main_delegate.cc b/android_webview/lib/main/aw_main_delegate.cc
index 303d808..daa77eb 100644
--- a/android_webview/lib/main/aw_main_delegate.cc
+++ b/android_webview/lib/main/aw_main_delegate.cc
@@ -51,6 +51,7 @@
   CommandLine* cl = CommandLine::ForCurrentProcess();
   bool zero_copy_disabled_by_switch = cl->HasSwitch(switches::kDisableZeroCopy);
   bool use_zero_copy = !zero_copy_disabled_by_switch &&
+                       cl->HasSwitch(switches::kEnableZeroCopy) &&
                        gpu_memory_buffer_factory_.get()->Initialize();
 
   if (use_zero_copy) {