More Valgrind 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 # running overnight and removing outdated bugs/suppressions.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 3512 matching lines @@
    fun:add_metadata_from_side_data
    fun:avcodec_decode_*
    fun:avcodec_decode_*
 }
 {
    bug_447788
    Memcheck:Unaddressable
    ...
    fun:_ZN3gpu5gles252GLES2ImplementationTest_TexImage3DSingleCommand_Test8TestBodyEv
 }
+{
+   bug_448700_a
+   Memcheck:Leak
+   fun:_Znw*
+   ...
+   fun:_ZN10extensions11ApiTestBase15RegisterModulesEv
+   fun:_ZN10extensions11ApiTestBase5SetUpEv
+}
+{
+   bug_448700_b
+   Memcheck:Leak
+   fun:_Znw*
+   ...
+   fun:_ZN10extensions12_GLOBAL__N_111TestNatives24GetObjectTemplateBuilderEPN2v87IsolateE
+   fun:_ZN3gin13WrappableBase14GetWrapperImplEPN2v87IsolateEPNS_11WrapperInfoE
+   fun:_ZN3gin9WrappableIN10extensions12_GLOBAL__N_111TestNativesEE10GetWrapperEPN2v87IsolateE
+   fun:_ZN3gin12CreateHandleIN10extensions12_GLOBAL__N_111TestNativesEEENS_6HandleIT_EEPN2v87IsolateEPS5_
+   fun:_ZN10extensions12_GLOBAL__N_111TestNatives6CreateEPN2v87IsolateERKN4base8CallbackIFvvEEE
+   fun:_ZN10extensions11ApiTestBase7RunTestERKSsS2_
+   fun:_ZN10extensions30MojoPrivateApiTest_Define_Test8TestBodyEv
+}