appcache: force-enable appcache for single process webview

This is a follow-up to this patch:
https://chromium-review.googlesource.com/c/chromium/src/+/2233709

Bug: 582750,1093785,1093780
Change-Id: I8940974cd474a48df7a2970e100caad6e3fab1fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2242119Reviewed-by: Richard Coles <torne@chromium.org>
Commit-Queue: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#777541}

android_webview/lib/aw_main_delegate.cc

@@ -127,6 +127,11 @@ bool AwMainDelegate::BasicStartupComplete(int* exit_code) {
   // metadata and controls.
   cl->AppendSwitch(switches::kDisableMediaSessionAPI);
 
+  // WebView does not support origin trials and so needs to force appcache
+  // to be enabled during the removal origin trial, until it is finally
+  // removed entirely.  See: http://crbug.com/582750
+  cl->AppendSwitch(switches::kAppCacheForceEnabled);
+
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
   if (cl->GetSwitchValueASCII(switches::kProcessType).empty()) {
     // Browser process (no type specified).