[Android] Uploading files takes increasingly more time as more files are uploaded

[Softvision-AndreeaCupsa]

[Notes]:

• The upload time increases once with the number of previously uploaded files.
• Uploading a file of 50MB with no previously uploaded files takes ~1:00, but uploading the same file after files 450MB were uploaded takes ~1:40.

[Affected Platforms]:

• Android 8.0.0 (Samsung S8, Huawei P20 Lite, Google Pixel)

[Prerequisites]:

• Have the latest Send Android application (org.mozilla.sendandroid-2019-02-20-release-signed.apk) installed on the device.

[Steps to reproduce]:

1. Open the Send application.
2. Upload a file of 50Mb and observe how much it takes to upload.
3. Upload the same file 8 more times.
4. Upload the file one last time and observe how much it takes to upload.

[Expected result]:
Step 2&4. Files take approximately the same time to upload.

[Actual result]:
Step 2&4. The file from Step 2 takes less time to upload than the one from Step 4.

[Additional notes]:

• This issue is not reproducible on the https://send2.dev.lcip.org website.
• Attached a screen recording with the issue: Link

[SoftVision-CosminMuntean]

I have retested this issue using the latest Android Send version (org.mozilla.sendandroid-2019-03-01-release-signed.apk) and the issue is still reproducible. The upload time increases once with the number of previously uploaded files.

Here are the testing results:

• On Google Pixel (Android 8.0.0) the first file (50 Mb) took ~1m15s to be uploaded. The same file uploaded 10th time took ~1m50s to be uploaded.
• On Samsung S8 (Android 8.0.0) the first file (50 Mb) took ~2:05s to be uploaded. The same file uploaded 10th time took ~2m 50s.