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

Review-Url: https://codereview.webrtc.org/2555483005
Cr-Commit-Position: refs/heads/master@{#15469}

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",