Add kEnableWebRtcHWVp8Encoding to GPU process.

VideoEncodeAccelerator::GetSupportedProfiles now runs in GPU
process because the profiles were added to GPUInfo. Add
kEnableWebRtcHWVp8Encoding to GPU process to fix the missing
encode profile.

BUG=418762
TEST=Run apprtc loopback and check the histogram.

Review URL: https://codereview.chromium.org/618633002

Cr-Commit-Position: refs/heads/master@{#297445}

content/browser/gpu/gpu_process_host.cc

@@ -80,6 +80,7 @@ static const char* const kSwitchNames[] = {
   switches::kDisableSeccompFilterSandbox,
 #if defined(ENABLE_WEBRTC)
   switches::kDisableWebRtcHWEncoding,
+  switches::kEnableWebRtcHWVp8Encoding,
 #endif
   switches::kEnableLogging,
   switches::kEnableShareGroupAsyncTextureUpload,