Init selection_text_offset_ in class constructor.

tools/valgrind/memcheck/suppressions.txt

Index: tools/valgrind/memcheck/suppressions.txt
diff --git a/tools/valgrind/memcheck/suppressions.txt b/tools/valgrind/memcheck/suppressions.txt
index 46917de087a8a3cf848ac3d54b5761d827f13f15..d3a655be7d42e233edc1e248fd94b0f31d927a32 100644
--- a/tools/valgrind/memcheck/suppressions.txt
+++ b/tools/valgrind/memcheck/suppressions.txt
@@ -4963,22 +4963,6 @@
    fun:_ZN7browser8NavigateEPNS_14NavigateParamsE
 }
 {
-   bug_101342
-   Memcheck:Cond
-   fun:_ZN14RenderViewImpl23SyncSelectionIfRequiredEv
-   fun:_ZN14RenderViewImpl18didChangeSelectionEb
-   fun:_ZN6WebKit16EditorClientImpl25respondToChangedSelectionEv
-   fun:_ZN7WebCore6Editor25respondToChangedSelectionERKNS_16VisibleSelectionE
-   fun:_ZN7WebCore6Editor25respondToChangedSelectionERKNS_16VisibleSelectionEj
-   fun:_ZN7WebCore14FrameSelection12setSelectionERKNS_16VisibleSelectionEjNS0_19CursorAlignOnScrollENS_15TextGranularityE
-   fun:_ZN7WebCore14FrameSelection12setSelectionERKNS_16VisibleSelectionENS_15TextGranularityE
-   fun:_ZN7WebCore14FrameSelection34setNonDirectionalSelectionIfNeededERKNS_16VisibleSelectionENS_15TextGranularityENS0_23EndPointsAdjustmentModeE
-   fun:_ZN7WebCore12EventHandler49updateSelectionForMouseDownDispatchingSelectStartEPNS_4NodeERKNS_16VisibleSelectionENS_15TextGranularityE
-   fun:_ZN7WebCore12EventHandler32handleMousePressEventSingleClickERKNS_28MouseEventWithHitTestResultsE
-   fun:_ZN7WebCore12EventHandler21handleMousePressEventERKNS_28MouseEventWithHitTestResultsE
-   fun:_ZN7WebCore12EventHandler21handleMousePressEventERKNS_18PlatformMouseEventE
-}
-{
    bug_101345
    Memcheck:Leak
    fun:_Znw*