Skip downloading zip files during installation if present

[kfrajer]

Summary:

When installing the AndroidSDK, it first downloads the needed zip files into the temp folder and then it creates the sdk/ folder and unzip them there. Finally it removes the temp folder that stores the zip files (Intended behavior)

Feature request:

To downloaded the files only if not present in the temp folder.

Additional info:

Currently this can be done manually by following these steps:

1. Download the files and place them in the temp folder
2. Disable the following two blocks:

• The while() block in downloadAndUnpack() function within SDKDownloader.java
• Disable removal of Temp folder in SDKDownloader.java. It is in the SDKDownloadTask class.

[DeerajTheepshi]

• I guess this might be useful in cases of an incomplete download due to, say internet connectivity , and the user might have to download all the zip files once again .
• In the downloadAndUnpack() method : We could check for the presence of temp folder (in case of incomplete downloads), check the files for md5 checksum and then unzip it .

[kfrajer]

Yes, I think this is a great use case and I like it. However there are other use cases that we need to capture. For example, Sarah's comment here, #21

The first step to implement this is for urlHolder to also manage file size and file checksum values.
The second step is to manage the temp/ folder lifecycle during installation.