[PIP] Add picture in picture flag and switch.

chrome/browser/flag_descriptions.cc

Index: chrome/browser/flag_descriptions.cc
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 3fe7dc57fa21a7f0e18e1cea0456c7f04e25e41e..9148d7468ed2db4f3bab46e4bbe716273402559b 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -1062,6 +1062,11 @@ const char kEnableNavigationTracingDescription[] =
     "flag. The trace may include personally identifiable information (PII) "
     "such as the titles and URLs of websites you visit.";
 
+const char kEnablePictureInPictureName[] = "Enable picture in picture.";
+
+const char kEnablePictureInPictureDescription[] =
+    "Enable the picture in picture feature for videos.";
+
 const char kTraceUploadUrlName[] = "Trace label for navigation tracing";
 
 const char kTraceUploadUrlDescription[] =