Fix way-over-allocation in pipe.

Fix way-over-allocation in pipe.

https://codereview.chromium.org/283093002 fixed some bugs in pipe memory
allocation, but also introduced one of its own: nearly every block requested
from needOpBytes() got its own 16K allocation.

The correct logic is to take the requested size, add four more bytes for a
DrawOp, make sure that's 4-byte aligned, then check to see if there's enough
space for that in the current block.  If there's not, allocate at least
MIN_BLOCK_SIZE bytes to fit the request.

The bug is that I moved that round-up-to-MIN_BLOCK_SIZE step before checking
for space in the current block.  This means most (all?) blocks will be 16K but
never seem to have room to fit another allocation.  You need 8 bytes?  You get
16K.  You need 8 more bytes?  Nope, can't fit that.  Here's a new 16K...

This reverts the change to the test I made then, which really should have
tipped me off.  It was testing exactly this bug.

BUG=372671
Committed: https://skia.googlesource.com/skia/+/6d88e6ce51ff34c99a1135161f06f29322f58e5a

[tomhudson, 2014-07-30 16:06:38]

lgtm

[commit-bot: I haz the power, 2014-07-30 16:07:20]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/mtklein@chromium.org/433463003/1

[commit-bot: I haz the power, 2014-07-30 16:18:01]

Change committed as 6d88e6ce51ff34c99a1135161f06f29322f58e5a