[TTS] Add a chrome://flags for client/server debug

Adds a new Feature ContextualSearchDebug that enables internal debugging
for the client and the server.  This should help us debug issues with
the Definitions feature and upcoming server-supported features.

This adds a flag to chrome://flags and will send an integration
code to the server to enable debugging for the backend requests.

We already have a mechanism to handle integration codes like this
but the server will need to be updated to handle this code for
debugging.

Hopefully the experimentation framework can send a bit automatically
to the server to indicate this debug feature is required for the
server request.  If that works we can simplify this code a bit.

Currently there is no client-side debugging enabled when this
flag is flipped, but we'll probably add some eventually.

BUG=1059004

Change-Id: Ib39911e410d36aa2ffc3874722885ba3a5cd5917
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2026421
Commit-Queue: Donn Denman <[email protected]>
Auto-Submit: Donn Denman <[email protected]>
Reviewed-by: Theresa  <[email protected]>
Cr-Commit-Position: refs/heads/master@{#748300}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index b196a38..a07d9e8 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1665,6 +1665,9 @@
      flag_descriptions::kHistoryManipulationInterventionDescription, kOsAll,
      FEATURE_VALUE_TYPE(features::kHistoryManipulationIntervention)},
 #if defined(OS_ANDROID)
+    {"contextual-search-debug", flag_descriptions::kContextualSearchDebugName,
+     flag_descriptions::kContextualSearchDebugDescription, kOsAndroid,
+     FEATURE_VALUE_TYPE(chrome::android::kContextualSearchDebug)},
     {"contextual-search-definitions",
      flag_descriptions::kContextualSearchDefinitionsName,
      flag_descriptions::kContextualSearchDefinitionsDescription, kOsAndroid,