Fix RenderTextTest.PangoAttributes test leaks; remove suppressions.

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 # running overnight and removing outdated bugs/suppressions.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 6548 matching lines @@
    fun:_ZN7WebCore18RenderLayerBacking*GraphicsLayer*
 }
 {
    bug_173356
    Memcheck:Overlap
    fun:memcpy
    fun:_ZN3gpu5gles2*Immediate4InitE*
    fun:_ZN3gpu5gles2*GLES2ImplementationTest_*_Test8TestBodyEv
 }
 {
-   bug_173597_a
-   Memcheck:Leak
-   fun:malloc
-   fun:g_malloc
-   fun:g_slice_alloc
-   fun:pango_attr_list_get_iterator
-   fun:_ZN3gfx35RenderTextTest_PangoAttributes_Test8TestBodyEv
-}
-{
-   bug_173597_b
-   Memcheck:Leak
-   fun:realloc
-   fun:g_realloc
-   fun:g_string_maybe_expand
-   fun:g_string_insert_len
-   fun:pango_font_description_to_string
-   fun:_ZN3gfx35RenderTextTest_PangoAttributes_Test8TestBodyEv
-}
-{
    bug_173620
    Memcheck:Uninitialized
    fun:_ZNK3net21HttpStreamFactoryImpl30GetAlternateProtocolRequestForERK4GURLPS1_
    fun:_ZN3net21HttpStreamFactoryImpl13RequestStreamERKNS_15HttpRequestInfoERKNS_9SSLConfigES6_PNS_17HttpStreamRequest8DelegateERKNS_11BoundNetLogE
    fun:_ZN3net22HttpNetworkTransaction14DoCreateStreamEv
    fun:_ZN3net22HttpNetworkTransaction6DoLoopEi
    fun:_ZN3net22HttpNetworkTransaction5StartEPKNS_15HttpRequestInfoERKN4base8CallbackIFviEEERKNS_11BoundNetLogE
    fun:_ZN3net12_GLOBAL__N_126GroupNameTransactionHelperERKSsRK13scoped_refptrINS_18HttpNetworkSessionEE
    fun:_ZN3net66HttpNetworkTransactionSpdy*Test_GroupNameForDirectConnections_Test8TestBodyEv
 }