Reland of Add framerate to VideoSinkWants and ability to signal on overuse (patchset #1 id:1 of https://codereview.webrtc.org/2783183003/ )

Reason for revert:
Seem to be a flaky test rather than an issue with this cl. Creating reland, will add code to reduce flakiness to that test.

Original issue's description:
> Revert of Add framerate to VideoSinkWants and ability to signal on overuse (patchset #8 id:410001 of https://codereview.webrtc.org/2781433002/ )
>
> Reason for revert:
> This has resulted in failure of CallPerfTest.ReceivesCpuOveruseAndUnderuse test on the Win7 build bot https://build.chromium.org/p/client.webrtc.perf/builders/Win7/builds/1780
>
> Original issue's description:
> > Reland of Add framerate to VideoSinkWants and ability to signal on overuse (patchset #1 id:1 of https://codereview.webrtc.org/2764133002/ )
> >
> > Reason for revert:
> > Found issue with test case, will add fix to reland cl.
> >
> > Original issue's description:
> > > Revert of Add framerate to VideoSinkWants and ability to signal on overuse (patchset #14 id:250001 of https://codereview.webrtc.org/2716643002/ )
> > >
> > > Reason for revert:
> > > Breaks perf tests:
> > > https://build.chromium.org/p/client.webrtc.perf/builders/Win7/builds/1679
> > > https://build.chromium.org/p/client.webrtc.perf/builders/Android32%20Tests%20%28L%20Nexus5%29/builds/2325
> > >
> > > Original issue's description:
> > > > Add framerate to VideoSinkWants and ability to signal on overuse
> > > >
> > > > In ViEEncoder, try to reduce framerate instead of resolution if the
> > > > current degradation preference is maintain-resolution rather than
> > > > balanced.
> > > >
> > > > BUG=webrtc:4172
> > > >
> > > > Review-Url: https://codereview.webrtc.org/2716643002
> > > > Cr-Commit-Position: refs/heads/master@{#17327}
> > > > Committed: https://chromium.googlesource.com/external/webrtc/+/72acf2526177bb4dbb5103cd6e165eb4361a5ae6
> > >
> > > TBR=nisse@webrtc.org,magjed@webrtc.org,kthelgason@webrtc.org,ilnik@webrtc.org,stefan@webrtc.org,sprang@webrtc.org
> > > # Skipping CQ checks because original CL landed less than 1 days ago.
> > > NOPRESUBMIT=true
> > > NOTREECHECKS=true
> > > NOTRY=true
> > > BUG=webrtc:4172
> > >
> > > Review-Url: https://codereview.webrtc.org/2764133002
> > > Cr-Commit-Position: refs/heads/master@{#17331}
> > > Committed: https://chromium.googlesource.com/external/webrtc/+/8b45b11144c968b4173215c76f78c710c9a2ed0b
> >
> > TBR=nisse@webrtc.org,magjed@webrtc.org,kthelgason@webrtc.org,ilnik@webrtc.org,stefan@webrtc.org,skvlad@webrtc.org
> > # Not skipping CQ checks because original CL landed more than 1 days ago.
> > BUG=webrtc:4172
> >
> > Review-Url: https://codereview.webrtc.org/2781433002
> > Cr-Commit-Position: refs/heads/master@{#17474}
> > Committed: https://chromium.googlesource.com/external/webrtc/+/3ea3c77e93121b1ab9d5e46641e6764f2cca0d51
>
> TBR=ilnik@webrtc.org,stefan@webrtc.org,asapersson@webrtc.org,sprang@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:4172
>
> Review-Url: https://codereview.webrtc.org/2783183003
> Cr-Commit-Position: refs/heads/master@{#17477}
> Committed: https://chromium.googlesource.com/external/webrtc/+/f9ed235c9b7248694edcb46feb1f29ce7456ab59

R=ilnik@webrtc.org,stefan@webrtc.org
BUG=webrtc:4172

Review-Url: https://codereview.webrtc.org/2789823002
Cr-Original-Commit-Position: refs/heads/master@{#17498}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: c5d62e29ca21da19a89c0a287c2d5231afa6465a
diff --git a/media/engine/webrtcvideoengine2.cc b/media/engine/webrtcvideoengine2.cc
index 8c3f958..742b34c 100644
--- a/media/engine/webrtcvideoengine2.cc
+++ b/media/engine/webrtcvideoengine2.cc
@@ -38,9 +38,10 @@
 #include "webrtc/video_decoder.h"
 #include "webrtc/video_encoder.h"
 
+using DegradationPreference = webrtc::VideoSendStream::DegradationPreference;
+
 namespace cricket {
 namespace {
-
 // If this field trial is enabled, we will enable sending FlexFEC and disable
 // sending ULPFEC whenever the former has been negotiated. Receiving FlexFEC
 // is enabled whenever FlexFEC has been negotiated.
@@ -1637,26 +1638,35 @@
   }
 
   if (source_ && stream_) {
-    stream_->SetSource(
-        nullptr, webrtc::VideoSendStream::DegradationPreference::kBalanced);
+    stream_->SetSource(nullptr, DegradationPreference::kDegradationDisabled);
   }
   // Switch to the new source.
   source_ = source;
   if (source && stream_) {
-    // Do not adapt resolution for screen content as this will likely
-    // result in blurry and unreadable text.
-    // |this| acts like a VideoSource to make sure SinkWants are handled on the
-    // correct thread.
-    stream_->SetSource(
-        this, enable_cpu_overuse_detection_ &&
-                      !parameters_.options.is_screencast.value_or(false)
-                  ? webrtc::VideoSendStream::DegradationPreference::kBalanced
-                  : webrtc::VideoSendStream::DegradationPreference::
-                        kMaintainResolution);
+    stream_->SetSource(this, GetDegradationPreference());
   }
   return true;
 }
 
+webrtc::VideoSendStream::DegradationPreference
+WebRtcVideoChannel2::WebRtcVideoSendStream::GetDegradationPreference() const {
+  // Do not adapt resolution for screen content as this will likely
+  // result in blurry and unreadable text.
+  // |this| acts like a VideoSource to make sure SinkWants are handled on the
+  // correct thread.
+  DegradationPreference degradation_preference;
+  if (!enable_cpu_overuse_detection_) {
+    degradation_preference = DegradationPreference::kDegradationDisabled;
+  } else {
+    if (parameters_.options.is_screencast.value_or(false)) {
+      degradation_preference = DegradationPreference::kMaintainResolution;
+    } else {
+      degradation_preference = DegradationPreference::kMaintainFramerate;
+    }
+  }
+  return degradation_preference;
+}
+
 const std::vector<uint32_t>&
 WebRtcVideoChannel2::WebRtcVideoSendStream::GetSsrcs() const {
   return ssrcs_;
@@ -2095,16 +2105,7 @@
   parameters_.encoder_config.encoder_specific_settings = NULL;
 
   if (source_) {
-    // Do not adapt resolution for screen content as this will likely result in
-    // blurry and unreadable text.
-    // |this| acts like a VideoSource to make sure SinkWants are handled on the
-    // correct thread.
-    stream_->SetSource(
-        this, enable_cpu_overuse_detection_ &&
-                      !parameters_.options.is_screencast.value_or(false)
-                  ? webrtc::VideoSendStream::DegradationPreference::kBalanced
-                  : webrtc::VideoSendStream::DegradationPreference::
-                        kMaintainResolution);
+    stream_->SetSource(this, GetDegradationPreference());
   }
 
   // Call stream_->Start() if necessary conditions are met.