Flip unified media pipeline to default-on w/ disabled holdback.

android_webview/lib/main/aw_main_delegate.cc

Index: android_webview/lib/main/aw_main_delegate.cc
diff --git a/android_webview/lib/main/aw_main_delegate.cc b/android_webview/lib/main/aw_main_delegate.cc
index cdc9ba59c08e6410ea67cd59bfd3264a5cc67ada..d110ad2e39a5b02b189ad692fc61375cf4e9505c 100644
--- a/android_webview/lib/main/aw_main_delegate.cc
+++ b/android_webview/lib/main/aw_main_delegate.cc
@@ -140,6 +140,10 @@ bool AwMainDelegate::BasicStartupComplete(int* exit_code) {
     cl->AppendSwitch(switches::kDisableRendererBackgrounding);
   }
 
+  // TODO(liberato, watk): Reenable after resolving fullscreen test failures.
+  // See http://crbug.com/597495
+  cl->AppendSwitch(switches::kDisableUnifiedMediaPipeline);
+
   return false;
 }