Add four new suppressions, widen one.

tools/valgrind/memcheck/suppressions_mac.txt

 # There are three kinds of suppressions in this file:
 # 1. Third party stuff we have no control over.
 #
 # 2. Intentional unit test errors, 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.
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 175 matching lines @@
    fun:_DPSNextEvent
    fun:-[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:]
    fun:-[NSApplication run]
 }
 {
    bug_18223
    Memcheck:Cond
    fun:_ZNK8Security12UnixPlusPlus17StaticForkMonitorclEv
    fun:_ZN12ocspdGlobals10serverPortEv
 }
+{
+   # Invalid read
+   bug_20508a
+   Memcheck:Addr4
+   ...
+   fun:ripc_DrawGlyphs
+   fun:draw_glyphs
+   fun:CGContextShowGlyphsWithAdvances
+}
+{
+   # Invalid read
+   bug_20508b
+   Memcheck:Addr4
+   fun:_eATSFontGetGlyphIDsForGlyphNames
+   fun:ATSFontGetGlyphIDsForGlyphNames
+   fun:ats_font_get_glyphs_for_glyph_names
+   fun:get_glyphs_for_glyph_names
+}
+
 
 # 2. Intentional unit test errors, stuff that is somehow a false positive
 # in our own code, or stuff that is so trivial it's not worth fixing.
 {
    # NSObject pointers in a static std::map; we do technically leak them, but
    # only on shutdown, so it's not worth fixing.
    static_theme_cache
    Memcheck:Leak
    fun:calloc
    fun:_internal_class_createInstanceFromZone
@@ skipping 287 matching lines @@
    fun:-[CIContextImpl render:]
    fun:cgxcoreimage_instance_render
    fun:CGXCoreImageInstanceRender
 }
 {
    bug_18984
    Memcheck:Free
    fun:_ZdlPv
    fun:_ZN7WebCore15CSSSelectorList19adoptSelectorVectorERN3WTF6VectorIPNS_11CSSSelectorELm0EEE
    ...
-   fun:_ZN7WebCore9CSSParser15createStyleRuleEPN3WTF6VectorIPNS_11CSSSelectorELm0EEE
    fun:_Z10cssyyparsePv
-   fun:_ZN7WebCore9CSSParser10parseSheetEPNS_13CSSStyleSheetERKNS_6StringE
 }
 {
    # Leak of a CFMutableArray of certs in X509Certificate::Verify.
    bug_20459
    Memcheck:Leak
    fun:malloc_zone_malloc
    fun:_CFRuntimeCreateInstance
    fun:__CFArrayInit
    fun:CFArrayCreateMutableCopy
    fun:_ZNK3net15X509Certificate6VerifyERKSsiPNS_16CertVerifyResultE
    fun:_ZN3net12CertVerifier7Request8DoVerifyEv
    fun:_ZN14RunnableMethodIN3net12CertVerifier7RequestEMS2_FvvE6Tuple0E3RunEv
    fun:-[TaskOperation main]
    fun:-[NSOperation start]
    fun:__runop
    fun:_pthread_wqthread
    fun:start_wqthread
 }
+{
+   bug_20504
+   Memcheck:Leak
+   fun:malloc_zone_calloc
+   fun:_internal_class_createInstanceFromZone
+   fun:+[NSObject allocWithZone:]
+   fun:-[NSCustomObject nibInstantiate]
+   fun:-[NSIBObjectData instantiateObject:]
+   fun:-[NSIBObjectData nibInstantiateWithOwner:topLevelObjects:]
+   fun:loadNib
+   fun:+[NSBundle(NSNibLoading) _loadNibFile:nameTable:withZone:ownerBundle:]
+   fun:+[NSBundle(NSNibLoading) loadNibFile:externalNameTable:withZone:]
+   fun:+[NSBundle(NSNibLoading) loadNibNamed:owner:]
+   fun:_ZN8Platform29WillInitializeMainMessageLoopERK18MainFunctionParams
+}