Increase DEFAULT_CHUNK_SIZE to reduce transfer overhead

[domZippilli]

Fixes#86 by setting the DEFAULT_CHUNK_SIZE to 15MiB.

[elharo]

Looks like this breaks com.google.cloud.BaseWriteChannelTest

[codecov]

Codecov Report

Merging #87 into master will increase coverage by 0.14%.
The diff coverage is n/a.

@@ Coverage Diff @@## master #87 +/- ##
============================================
+ Coverage 66.32% 66.46% +0.14% + Complexity 367 362 -5 
============================================
Files 34 34 Lines 1865 1858 -7 Branches 236 234 -2 ============================================
- Hits 1237 1235 -2 + Misses 526 521 -5 
Partials 102 102

Impacted Files	Coverage Δ	Complexity Δ
...c/main/java/com/google/cloud/BaseWriteChannel.java	36.5% <ø> (ø)	18 <0> (ø)	⬇️
.../com/google/cloud/MonitoredResourceDescriptor.java	83.76% <0%> (-0.28%)	20% <0%> (-4%)
...a/com/google/cloud/testing/BaseEmulatorHelper.java	31.21% <0%> (-0.22%)	5% <0%> (ø)
...src/main/java/com/google/cloud/ServiceOptions.java	41.66% <0%> (+0.75%)	29% <0%> (-1%)	⬇️
...re/src/main/java/com/google/cloud/RetryHelper.java	53.84% <0%> (+3.84%)	2% <0%> (ø)	⬇️

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[frankyn]

LGTM. Thanks @domZippilli!

[domZippilli]

Hey just wanted to check in -- are there any steps I need to take to move this forward?

[elharo]

@frankyn FYI, you need to select the approve button in Github. Unlike google3, LGTM in a comment doesn't suffice.

[frankyn]

I did approve, but my approval doesn't count IIUC. Also I can't merge, could you help merge the PR as well @elharo?