Add command line switch to enable the Live Caption pref

This CL adds a command line switch that enables the kLiveCaptionEnabled
preference which will make it easier to add Swarming tests.

Bug: 1122784
Change-Id: I27f0f4ae4a0b19b97f454336f1ca5f372b1e50cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2382961Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Evan Liu <evliu@google.com>
Cr-Commit-Position: refs/heads/master@{#803205}

chrome/browser/accessibility/caption_controller.cc

@@ -7,6 +7,7 @@
 #include <string>
 
 #include "base/bind.h"
+#include "base/command_line.h"
 #include "base/feature_list.h"
 #include "base/metrics/histogram_functions.h"
 #include "chrome/browser/accessibility/caption_util.h"
@@ -66,6 +67,12 @@ void CaptionController::Init() {
 
   pref_change_registrar_ = std::make_unique<PrefChangeRegistrar>();
   pref_change_registrar_->Init(profile_->GetPrefs());
+  auto* command_line = base::CommandLine::ForCurrentProcess();
+  if (command_line &&
+      command_line->HasSwitch(switches::kEnableLiveCaptionPrefForTesting)) {
+    profile_->GetPrefs()->SetBoolean(prefs::kLiveCaptionEnabled, true);
+  }
+
   pref_change_registrar_->Add(
       prefs::kLiveCaptionEnabled,
       base::BindRepeating(&CaptionController::OnLiveCaptionEnabledChanged,

media/base/media_switches.cc

@@ -183,6 +183,10 @@ const char kOverrideEnabledCdmInterfaceVersion[] =
 const char kOverrideHardwareSecureCodecsForTesting[] =
     "override-hardware-secure-codecs-for-testing";
 
+// Sets the default value for the kLiveCaptionEnabled preference to true.
+const char kEnableLiveCaptionPrefForTesting[] =
+    "enable-live-caption-pref-for-testing";
+
 #if defined(OS_CHROMEOS)
 // ChromeOS uses one of two VideoDecoder implementations based on SoC/board
 // specific configurations that are signalled via this command line flag.

media/base/media_switches.h

@@ -85,6 +85,7 @@ MEDIA_EXPORT extern const char kMSEVideoBufferSizeLimitMb[];
 MEDIA_EXPORT extern const char kClearKeyCdmPathForTesting[];
 MEDIA_EXPORT extern const char kOverrideEnabledCdmInterfaceVersion[];
 MEDIA_EXPORT extern const char kOverrideHardwareSecureCodecsForTesting[];
+MEDIA_EXPORT extern const char kEnableLiveCaptionPrefForTesting[];
 
 namespace autoplay {