Simplify ZoomController by removing DefaultZoomLevel prefs machinery.

Simplify ZoomController by removing DefaultZoomLevel prefs machinery.

In preparation for moving to multiple HostZoomMaps (one-per
StoragePartition), it is helpful to simplify ZoomController by removing
the prefs machinery for DefaultZoomLevel, and instead rely on getting
this value from the HostZoomMap.

The calls to ZoomController::UpdateState() that used to be triggered
directly by the prefs changes still occur, though by a roundtrip from
PrefsTabHelper via IPC to RenderViewImpl and then by IPC back to
the HostZoomMap, which in turn notifies its observers. This only happens
in cases where the change in DefaultZoomLevel actually causes the
RenderViewImpl to change its zoom, so it is a subtle change in behaviour
from before.

BUG=335317
Committed: https://crrev.com/32a991c969d22f900e0b234b7c2653cc79cc2aeb
Cr-Commit-Position: refs/heads/master@{#292920}

[wjmaclean, 2014-08-27 18:42:34]

wjmaclean@chromium.org changed reviewers:
+ dbeam@chromium.org

[wjmaclean, 2014-08-27 18:51:30]

dbeam@ - since this involves a subtle behavioural change, would you mind taking
a look?

The change is this: 

** Before this CL:

ZoomController::UpdateState is called every time DefaultZoomLevel changes, and
sends a ZoomObserver event (which always has can_show_bubble = false, and in
which the zoom level may not have changed).

** After this CL

ZoomController::UpdateState is only called if the associated RenderView actually
changes its zoom level in response to the change in DefaultZoomLevel, meaning
ZoomObserver events are only sent if the zoom level actually changed.

[Dan Beam, 2014-08-27 22:46:09]

lgtm

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
File chrome/browser/ui/zoom/zoom_controller.h (right):

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
chrome/browser/ui/zoom/zoom_controller.h:78: return
content::HostZoomMap::GetDefaultForBrowserContext(browser_context_)
-> at end

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
File chrome/browser/ui/zoom/zoom_controller_browsertest.cc (right):

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
chrome/browser/ui/zoom/zoom_controller_browsertest.cc:41: void Wait() {
message_loop_runner_->Run(); }
nit: \n

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
chrome/browser/ui/zoom/zoom_controller_browsertest.cc:63: protected:
nit: i'd say make public accessors with private member

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
chrome/browser/ui/zoom/zoom_controller_browsertest.cc:113: // TODO(wjmaclean)
Convert this to call partition-specific zoom level prefs
add colon, e.g., TODO(wjmaclean): Convert

[wjmaclean, 2014-09-02 13:05:13]

Cleaned up patch for landing.

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
File chrome/browser/ui/zoom/zoom_controller.h (right):

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
chrome/browser/ui/zoom/zoom_controller.h:78: return
content::HostZoomMap::GetDefaultForBrowserContext(browser_context_)
On 2014/08/27 22:46:09, Dan Beam wrote:
> -> at end

Done.

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
File chrome/browser/ui/zoom/zoom_controller_browsertest.cc (right):

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
chrome/browser/ui/zoom/zoom_controller_browsertest.cc:41: void Wait() {
message_loop_runner_->Run(); }
On 2014/08/27 22:46:09, Dan Beam wrote:
> nit: \n

Done.

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
chrome/browser/ui/zoom/zoom_controller_browsertest.cc:63: protected:
On 2014/08/27 22:46:09, Dan Beam wrote:
> nit: i'd say make public accessors with private member

Just realized we aren't using this anyway, so removed it.

https://codereview.chromium.org/508263002/diff/1/chrome/browser/ui/zoom/zoom_...
chrome/browser/ui/zoom/zoom_controller_browsertest.cc:113: // TODO(wjmaclean)
Convert this to call partition-specific zoom level prefs
On 2014/08/27 22:46:09, Dan Beam wrote:
> add colon, e.g., TODO(wjmaclean): Convert

Done.

[wjmaclean, 2014-09-02 13:05:16]

The CQ bit was checked by wjmaclean@chromium.org

[commit-bot: I haz the power, 2014-09-02 13:06:16]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/wjmaclean@chromium.org/508263002/20001

[commit-bot: I haz the power, 2014-09-02 14:15:57]

Committed patchset #2 (id:20001) as 95211d14f66c27c5d309fcf985a6049fd32900c0

[commit-bot: I haz the power, 2014-09-10 03:18:18]

Patchset 2 (id:??) landed as
https://crrev.com/32a991c969d22f900e0b234b7c2653cc79cc2aeb
Cr-Commit-Position: refs/heads/master@{#292920}