Reland of Add ability to scale to arbitrary factors (patchset #1 id:1 of https://codereview.webrtc.org/2557323002/ )

Reason for revert:
There was a bug in the implementation where the adapter could get stuck at really low resolutions. That has now been fixed.

Original issue's description:
> Revert of Add ability to scale to arbitrary factors (patchset #7 id:120001 of https://codereview.webrtc.org/2555483005/ )
>
> Reason for revert:
> Issue discovered with scaling back up.
>
> Original issue's description:
> > Add ability to scale to arbitrary factors
> >
> > This CL adds a fallback for the case when no optimized scale factor produces a low enough resolution for what was requested. It also ensures that all resolutions provided by the video adapter are divisible by four. This is required by some hardware implementations.
> >
> > BUG=webrtc:6837
> >
> > Committed: https://crrev.com/710c335d785b104bda4a912bd7909e4d27f9b04f
> > Cr-Commit-Position: refs/heads/master@{#15469}
>
> TBR=magjed@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:6837
>
> Committed: https://crrev.com/7722a4cc8d31e5e924e9e6c5c97412ce8bbbe59d
> Cr-Commit-Position: refs/heads/master@{#15470}

R=magjed@webrtc.org
BUG=webrtc:6837,webrtc:6848

Review-Url: https://codereview.webrtc.org/2558243003
Cr-Commit-Position: refs/heads/master@{#15485}

webrtc/sdk/android/src/jni/androidvideotracksource.cc

@@ -12,13 +12,19 @@
 
 #include <utility>
 
+namespace {
+// MediaCodec wants resolution to be divisible by 2.
+const int kRequiredResolutionAlignment = 2;
+}
+
 namespace webrtc {
 
 AndroidVideoTrackSource::AndroidVideoTrackSource(rtc::Thread* signaling_thread,
                                                  JNIEnv* jni,
                                                  jobject j_egl_context,
                                                  bool is_screencast)
-    : signaling_thread_(signaling_thread),
+    : AdaptedVideoTrackSource(kRequiredResolutionAlignment),
+      signaling_thread_(signaling_thread),
       surface_texture_helper_(webrtc_jni::SurfaceTextureHelper::create(
           jni,
           "Camera SurfaceTextureHelper",