Make sure AllowRepaintScope::m_originalValue is always initialized

Make sure AllowRepaintScope::m_originalValue is always initialized

Make sure AllowRepaintScope::m_originalValue is always initialized. This fixes a
build error with gcc 4.8:
"""
core/frame/FrameView.h:567:65: error: ‘*((void*)& scoper +8)’ may be used
uninitialized in this function [-Werror=maybe-uninitialized]
"""

R=abarth@chromium.org, abarth, eseidel

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=166885

[Inactive, 2014-02-11 01:00:12]

The full build error is:
"""
In file included from
../../third_party/WebKit/Source/core/rendering/RenderLayerScrollableArea.cpp:55:0:
../../third_party/WebKit/Source/core/frame/FrameView.h: In member function ‘void
WebCore::RenderLayerScrollableArea::updateAfterLayout()’:
../../third_party/WebKit/Source/core/frame/FrameView.h:567:65: error:
‘*((void*)& scoper +8)’ may be used uninitialized in this function
[-Werror=maybe-uninitialized]
         m_view->setCanRepaintDuringPerformLayout(m_originalValue);
                                                                 ^
../../third_party/WebKit/Source/core/rendering/RenderLayerScrollableArea.cpp:635:27:
note: ‘*((void*)& scoper +8)’ was declared here
         AllowRepaintScope scoper(m_box->view()->frameView());
                           ^
cc1plus: all warnings being treated as errors
"""

I believe it started happening after:
https://src.chromium.org/viewvc/blink?revision=166872&view=revision

[Inactive, 2014-02-11 01:01:51]

+dsinclair in cc

[abarth-chromium, 2014-02-11 01:07:57]

lgtm

[Inactive, 2014-02-11 01:40:35]

Committed patchset #2 manually as r166885 (presubmit successful).