Initialize LayoutTableCell.is_spanning_collapsed_row_ to avoid MSAN error

TBR: joysyu@google.com
Bug: 751407
Change-Id: I3bb805d6f6c2a555925ce3ccf514e1e4b2d8df0a
Reviewed-on: https://chromium-review.googlesource.com/597031Reviewed-by: Tsuyoshi Horo <horo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491295}

third_party/WebKit/Source/core/layout/LayoutTableCell.cpp

@@ -60,6 +60,7 @@ LayoutTableCell::LayoutTableCell(Element* element)
     : LayoutBlockFlow(element),
       absolute_column_index_(kUnsetColumnIndex),
       cell_width_changed_(false),
+      is_spanning_collapsed_row_(false),
       collapsed_border_values_valid_(false),
       intrinsic_padding_before_(0),
       intrinsic_padding_after_(0) {