Delete HostDelegate objects instead of HostImpl objects to avoid leaking the former.

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 # running overnight and removing outdated bugs/suppressions.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 5882 matching lines @@
 }
 {
    bug_116580
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN4base5Value18CreateIntegerValueEi
    fun:_ZNK4test3api21additional_properties26ReturnAdditionalProperties6Result12ResultObject7ToValueEv
    fun:_ZN4test3api21additional_properties26ReturnAdditionalProperties6Result6CreateERKNS3_12ResultObjectE
    fun:_ZN86JsonSchemaCompilerAdditionalPropertiesTest_ReturnAdditionalPropertiesResultCreate_Test8TestBodyEv
 }
-{
-   bug_116744
-   Memcheck:Leak
-   fun:_Znw*
-   fun:_ZN14GpuProcessHost12GetForClientEiN7content17CauseForGpuLaunchE
-}
 
 #-----------------------------------------------------------------------
 # 4. These only occur on our Google workstations
 
 {
    bug_todo_getdelim
    Memcheck:Leak
    fun:malloc
    fun:getdelim
    ...
    fun:call_init
    fun:_dl_init
 }
 {
    bug_todo_getdelim2
    Memcheck:Leak
    fun:malloc
    fun:getdelim
    obj:/lib/libselinux.so.1
    obj:/lib/libselinux.so.1
    obj:/lib/libselinux.so.1
 }
 {
    bug_todo_grep
    Memcheck:Leak
    fun:malloc
    obj:/bin/grep
    obj:/bin/grep
 }