Add a command-line option to enable VP9 encoding.

remoting/host/chromoting_host.cc

Index: remoting/host/chromoting_host.cc
diff --git a/remoting/host/chromoting_host.cc b/remoting/host/chromoting_host.cc
index 469c5b2849f824a9c2235a1fa705baddafe028b0..35e8800562dc0a349306e17d5ea5b9e890593895 100644
--- a/remoting/host/chromoting_host.cc
+++ b/remoting/host/chromoting_host.cc
@@ -8,6 +8,7 @@
 
 #include "base/bind.h"
 #include "base/callback.h"
+#include "base/command_line.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "build/build_config.h"
 #include "remoting/base/constants.h"
@@ -29,6 +30,8 @@ namespace remoting {
 
 namespace {
 
+const char kEnableVp9SwitchName[] = "enable-vp9";
+
 const net::BackoffEntry::Policy kDefaultBackoffPolicy = {
   // Number of initial errors (in sequence) to ignore before applying
   // exponential back-off rules.
@@ -86,9 +89,11 @@ ChromotingHost::ChromotingHost(
   DCHECK(network_task_runner_->BelongsToCurrentThread());
   DCHECK(signal_strategy);
 
-  // VP9 encode is not yet supported.
-  protocol::CandidateSessionConfig::DisableVideoCodec(
-      protocol_config_.get(), protocol::ChannelConfig::CODEC_VP9);
+  // Disable VP9 unless it is explicitly enabled via the command-line.
+  if (!CommandLine::ForCurrentProcess()->HasSwitch(kEnableVp9SwitchName)) {
+    protocol::CandidateSessionConfig::DisableVideoCodec(
+        protocol_config_.get(), protocol::ChannelConfig::CODEC_VP9);
+  }
 
   if (!desktop_environment_factory_->SupportsAudioCapture()) {
     protocol::CandidateSessionConfig::DisableAudioChannel(