Add support for scaling textures in AndroidVideoCapturer.

The idea is to also reuse AndroidTextureBuffer::CropAndScale when scaling in the encoder.

BUG=webrtc:4993
R=magjed@webrtc.org

Review URL: https://codereview.webrtc.org/1471333003 .

Cr-Commit-Position: refs/heads/master@{#10802}

talk/app/webrtc/java/jni/native_handle_impl.h

@@ -54,6 +54,12 @@ class AndroidTextureBuffer : public webrtc::NativeHandleBuffer {
   ~AndroidTextureBuffer();
   rtc::scoped_refptr<VideoFrameBuffer> NativeToI420Buffer() override;
 
+  rtc::scoped_refptr<AndroidTextureBuffer> CropAndScale(
+      int cropped_input_width,
+      int cropped_input_height,
+      int dst_widht,
+      int dst_height);
+
  private:
   NativeHandleImpl native_handle_;
   rtc::Callback0<void> no_longer_used_cb_;