Fix tab switch time regression from backgrounded renderers change

Fix tab switch time regression from backgrounded renderers change

Switching between tabs is slightly slower after making it possible for
the browser to background hidden renderers. It appears the current
event sequence is to background the renderer and then have it free up
its resources in the GPU process. However in the background state it
runs slower and has its I/O throttled, slowing its interaction with
the GPU process. This slowdown in turn delays the newly-foregrounded
tab's GPU commands, resulting in increased tab switch times.

This change reverses the sequence of events that occur when a tab
is no longer foreground, freeing resources with the GPU before
putting the renderer in the background. This allows the renderer
to interact with the GPU at full speed, and complete its cleanup
before the newly-foregrounded tab begins issuing commands to the GPU,
restoring original tab switch times.

BUG=502502
Committed: https://crrev.com/a57db5090fe6a56c17a73bb5adc7562411840ae4
Cr-Commit-Position: refs/heads/master@{#335525}

[shrike, 2015-06-20 00:12:43]

shrike@chromium.org changed reviewers:
+ asvitkine@chromium.org

[shrike, 2015-06-22 17:10:56]

Hello asvitkine,

PTAL

[Alexei Svitkine (slow), 2015-06-22 17:13:17]

lgtm

https://codereview.chromium.org/1199543003/diff/1/content/browser/renderer_ho...
File content/browser/renderer_host/render_widget_host_view_mac.mm (right):

https://codereview.chromium.org/1199543003/diff/1/content/browser/renderer_ho...
content/browser/renderer_host/render_widget_host_view_mac.mm:912:
SuspendBrowserCompositorView();
Nit: Since the order is significant, please add a comment.

[shrike, 2015-06-22 17:34:22]

The CQ bit was checked by shrike@chromium.org

[shrike, 2015-06-22 17:34:23]

The patchset sent to the CQ was uploaded after l-g-t-m from
asvitkine@chromium.org
Link to the patchset: https://codereview.chromium.org/1199543003/#ps40001
(title: "Edit comment.")

[commit-bot: I haz the power, 2015-06-22 17:35:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1199543003/40001

[commit-bot: I haz the power, 2015-06-22 18:11:22]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-06-22 18:12:09]

Patchset 3 (id:??) landed as
https://crrev.com/a57db5090fe6a56c17a73bb5adc7562411840ae4
Cr-Commit-Position: refs/heads/master@{#335525}