[Chromium] Add a setting to control scaling content to fit viewport

[Chromium] Add a setting to control scaling content to fit viewport
https://bugs.webkit.org/show_bug.cgi?id=109584

Adds a setting called 'initializeAtMinimumPageScale'. By default,
it is set to 'true' which corresponds to Chrome on Android behavior--
adjust the page scale to make the content fit into the viewport
by width. When set to false, the setting instructs ChromeClientImpl to
set page scale to 1.0, unless the scale value is set by the page
in the viewport meta-tag.

Reviewed by Adam Barth.

* public/WebSettings.h:
* src/ChromeClientImpl.cpp:
(WebKit::ChromeClientImpl::dispatchViewportPropertiesDidChange):
* src/WebSettingsImpl.cpp:
(WebKit::WebSettingsImpl::WebSettingsImpl):
(WebKit::WebSettingsImpl::setInitializeAtMinimumPageScale):
(WebKit):
* src/WebSettingsImpl.h:
(WebSettingsImpl):
(WebKit::WebSettingsImpl::initializeAtMinimumPageScale):
* tests/WebFrameTest.cpp:
* tests/data/viewport-2x-initial-scale.html: Added.
* tests/data/viewport-auto-initial-scale.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@142875 268f45cc-cd09-0410-ab3c-d52691b4dbfc