Enable PDF+OOPIF by default on ToT

In order to continue with the launch process for this feature, we need
it to be enabled by default on tip-of-tree.

Bug: 659750
Change-Id: Ia55037944bde87793a6f1eb4fd6b83a5b2b362d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1764433
Commit-Queue: James MacLean <wjmaclean@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689423}

content/public/common/content_features.cc

@@ -256,7 +256,7 @@ const base::Feature kMediaDevicesSystemMonitorCache {
 // Instead of BrowserPlugin or GuestViews, MimeHandlerView will use a cross
 // process frame to render its handler.
 const base::Feature kMimeHandlerViewInCrossProcessFrame{
-    "MimeHandlerViewInCrossProcessFrame", base::FEATURE_DISABLED_BY_DEFAULT};
+    "MimeHandlerViewInCrossProcessFrame", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enables/disables the video capture service.
 const base::Feature kMojoVideoCapture{"MojoVideoCapture",