Init selection_text_offset_ in class constructor.

tools/valgrind/memcheck/suppressions.txt

 # There are four kinds of suppressions in this file.
 # 1. third party stuff we have no control over
 #
 # 2. intentional unit test errors, or stuff that is somehow a false positive
 # in our own code, or stuff that is so trivial it's not worth fixing
 #
 # 3. Suppressions for real chromium bugs that are not yet fixed.
 # These should all be in chromium's bug tracking system (but a few aren't yet).
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 4945 matching lines @@
    fun:_ZN21RenderViewHostManager14InitRenderViewEP14RenderViewHostRK15NavigationEntry
    fun:_ZN21RenderViewHostManager8NavigateERK15NavigationEntry
    fun:_ZN11TabContents15NavigateToEntryERK15NavigationEntryN20NavigationController10ReloadTypeE
    fun:_ZN11TabContents22NavigateToPendingEntryEN20NavigationController10ReloadTypeE
    fun:_ZN20NavigationController22NavigateToPendingEntryENS_10ReloadTypeE
    fun:_ZN20NavigationController9LoadEntryEP15NavigationEntry
    fun:_ZN20NavigationController7LoadURLERK4GURLS2_N7content14PageTransitionERKSs
    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*
    fun:_ZN22WebPluginDelegateProxy20CreateResourceClientEmRK4GURLi
    fun:_ZN6webkit5npapi13WebPluginImpl24HandleURLRequestInternalEPKcS3_S3_S3_jibNS1_8ReferrerEbb
 }
 {
    bug_101347
    Memcheck:Leak
    fun:_Znw*
@@ skipping 26 matching lines @@
 }
 {
    bug_todo_getdelim2
    Memcheck:Leak
    fun:malloc
    fun:getdelim
    obj:/lib/libselinux.so.1
    obj:/lib/libselinux.so.1
    obj:/lib/libselinux.so.1
 }