Use the default dispatcher where possible for nested message loops.

This is a re-land of crrev.com/256666.

* SimpleMessageBoxViews is no longer MessagePumpDispatcher.
The default dispatcher is used instead, and QuitNestedMessageLoop()
is called to terminate the loop instead of returning
POST_DISPATCH_QUIT_LOOP from the Dispatch() override.

* Always use dialog widget window's dispatcher-client.
There is no compelling reason for choosing the parent's dispatcher-
client over the dialog's dispatcher-client. Furthermore choosing
the wrong dispatcher-client causes a CHECK failure in WinDbg
interactive_ui_tests:CloseWithModalDialog.

R=sadrul@chromium.org
TBR=msw@chromium.org, sadrul@chromium.org, sky@chromium.org

BUG=351393
TEST=trybot and manual testing on Chrome OS.

Review URL: https://codereview.chromium.org/195763014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257032 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 257032
Cast: Use difference encoding on RTP timestamps for serializing events

Previously during serialization of raw event logs we write out RTP
timestamp of each frame as a relative value to the first RTP timestamp
seen. This number can get large for later frames. This patch changes
the serialization logic so it writes out the RTP timestamp of each
frame as a relative value to the previous frame. This results in smaller
values being written out for each frame, which results in a smaller
serialization length due to variable length encoding.

The result of this change is that serialized length with compression is
now 19% shorter. (86.5kb vs 70kb for 30 seconds of data)

Test: SerializeDeserializeTest still passes

BUG=338574,301920

Review URL: https://codereview.chromium.org/195943011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257035 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 257035
Improve some requestAutocomplete UMA metrics.

BUG=none

Review URL: https://codereview.chromium.org/183883029

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257036 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 257036