Clean up logic flow in OffscreenCanvasFrameDispatcher

Clean up logic flow in OffscreenCanvasFrameDispatcher

This CL causes no behavior change.

BUG=563852
Committed: https://crrev.com/6482715536e43777022b2e63e3f2a1247c8d4a00
Cr-Commit-Position: refs/heads/master@{#424020}

[xlai (Olivia), 2016-10-07 16:23:52]

xlai@chromium.org changed reviewers:
+ junov@chromium.org, xidachen@chromium.org

[xlai (Olivia), 2016-10-07 16:23:53]

I don't mean to change the code but when I was trying to
draw a logic flow of different cases in OffscreenCanvas.commit()
for another different matter, I find it super hard to follow
the long chain of if..else.. as well as the name of different
functions that prepare the TransferableResource. I have to 
write up a true/false table on sketch paper to understand what's
going on.

So I did the following:
1. For the individual functions, I renamed it to explicitly
   mention the type of object that is heavily playing a role
   in preparing the TransferableResource. In the software
   rendering case, it is inevitably the SharedBitmap; in the
   accelerated case, it is the StaticBitmap; in the "canvas
   not texture-backed but compositor is gpu-accelerated" case,
   I can see GPUSharedContext is playing an important role there
   and hence the name. Also, I'm trying to make three functions
   consistent by having a similar comment "Hold ref to..." at the
   end to make it clear to readers of what things are kept in
   hashmaps in this class.

2. I condense the current four "if/else" statements into three
   "if/else" statements and move the "Case X: ..." comments inside
    the if else block to make it clear. Also, I tried to put the
   non-negative boolean variable in the first if condition as this
   is a easier way to read the logic. 

I have done gpu integration texts on all pixel tests and confirm
that the image generated are exactly same as the reference images
on the cloud.

[xidachen, 2016-10-07 17:20:09]

lgtm

[Justin Novosad, 2016-10-07 17:37:14]

On 2016/10/07 17:20:09, xidachen wrote:
> lgtm

lgtm

[xidachen, 2016-10-07 19:39:07]

The CQ bit was checked by xidachen@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-10-07 19:39:34]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[xlai (Olivia), 2016-10-07 22:37:24]

The CQ bit was unchecked by xlai@chromium.org

[xlai (Olivia), 2016-10-07 23:52:52]

The CQ bit was checked by xlai@chromium.org

[commit-bot: I haz the power, 2016-10-07 23:53:10]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-07 23:59:10]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-10-08 00:03:10]

Description was changed from

==========
Clean up logic flow in OffscreenCanvasFrameDispatcher

This CL causes no behavior change.

BUG=563852
==========

to

==========
Clean up logic flow in OffscreenCanvasFrameDispatcher

This CL causes no behavior change.

BUG=563852

Committed: https://crrev.com/6482715536e43777022b2e63e3f2a1247c8d4a00
Cr-Commit-Position: refs/heads/master@{#424020}
==========

[commit-bot: I haz the power, 2016-10-08 00:03:11]

Patchset 1 (id:??) landed as
https://crrev.com/6482715536e43777022b2e63e3f2a1247c8d4a00
Cr-Commit-Position: refs/heads/master@{#424020}