Re-add kUseGpuInTests flag in WebRTC browser tests.

This reverts the removal of the kUseGpuInTests flags done in
https://crrev.com/cf04d9696a7f1f321294bc0970037ddb23c1204d
since it seems this affected performance results.
It also adds it to the new chrome/browser/media/chrome_webrtc_simulcast_browsertest.cc
test.

BUG=452654,452655

Review URL: https://codereview.chromium.org/879223002

Cr-Commit-Position: refs/heads/master@{#313475}

chrome/browser/media/chrome_webrtc_apprtc_browsertest.cc

@@ -55,8 +55,10 @@ class WebRtcApprtcBrowserTest : public WebRtcTestBase {
   void SetUpCommandLine(base::CommandLine* command_line) override {
     EXPECT_FALSE(command_line->HasSwitch(switches::kUseFakeUIForMediaStream));
 
-    // Use fake devices in order to run on VMs.
-    command_line->AppendSwitch(switches::kUseFakeDeviceForMediaStream);
+    // The video playback will not work without a GPU, so force its use here.
+    command_line->AppendSwitch(switches::kUseGpuInTests);
+    base::CommandLine::ForCurrentProcess()->AppendSwitch(
+        switches::kUseFakeDeviceForMediaStream);
   }
 
   void TearDown() override {

chrome/browser/media/chrome_webrtc_simulcast_browsertest.cc

@@ -33,6 +33,9 @@ class WebRtcSimulcastBrowserTest : public WebRtcTestBase {
     // Just answer 'allow' to GetUserMedia invocations.
     command_line->AppendSwitch(switches::kUseFakeUIForMediaStream);
 
+    // The video playback will not work without a GPU, so force its use here.
+    command_line->AppendSwitch(switches::kUseGpuInTests);
+
     // Use fake devices in order to run on VMs.
     command_line->AppendSwitch(switches::kUseFakeDeviceForMediaStream);
   }

chrome/browser/media/chrome_webrtc_video_quality_browsertest.cc

@@ -116,6 +116,9 @@ class WebRtcVideoQualityBrowserTest : public WebRtcTestBase,
     command_line->AppendSwitchPath(switches::kUseFileForFakeVideoCapture,
                                    webrtc_reference_video_y4m_);
     command_line->AppendSwitch(switches::kUseFakeDeviceForMediaStream);
+
+    // The video playback will not work without a GPU, so force its use here.
+    command_line->AppendSwitch(switches::kUseGpuInTests);
   }
 
   // Writes all frames we've captured so far by grabbing them from the