Heapcheck: Undo accidental suppression removals from r223350.

tools/heapcheck/suppressions.txt

 # There are three 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 # running overnight and removing outdated bugs/suppressions.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 871 matching lines @@
    bug_289719_c
    Heapcheck:Leak
    fun:__gnu_cxx::new_allocator::allocate
    fun:std::_Vector_base::_M_allocate
    fun:_Vector_base
    fun:vector
    fun:SafeBrowsingCheck
    fun:SafeBrowsingDatabaseManagerTest::RunSBHashTest
    fun:SafeBrowsingDatabaseManagerTest_CheckCorrespondsListType_Test::TestBody
 }
+{
+   bug_2912
+   Heapcheck:Leak
+   fun:v8::internal::Malloced::New
+   fun:v8::internal::Zone::NewSegment
+   fun:v8::internal::Zone::NewExpand
+   fun:v8::internal::Zone::New
+   fun:v8::internal::ZoneAllocationPolicy::New
+   fun:v8::internal::List::NewData
+   fun:v8::internal::List::Resize
+}
+{
+   bug_291236_b
+   Heapcheck:Leak
+   fun:v8::internal::Malloced::New
+   fun:v8::internal::Zone::NewSegment
+   fun:v8::internal::Zone::NewExpand
+   fun:v8::internal::Zone::New
+   fun:v8::internal::ZoneObject::operator new
+   fun:v8::internal::HOptimizedGraphBuilder::VisitCompareOperation
+   fun:v8::internal::CompareOperation::Accept
+   fun:v8::internal::HOptimizedGraphBuilder::Visit
+   fun:v8::internal::HOptimizedGraphBuilder::VisitForControl
+}