Update from https://crrev.com/316786

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 # running overnight and removing outdated bugs/suppressions.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 191 matching lines @@
    ...
    fun:img_data_lock
    fun:CGSImageDataLock
    fun:ripc_AcquireImage
    fun:ripc_DrawImage*
    fun:CGContextDrawImage*
    ...
    fun:_ZN11CUIRenderer4DrawE6CGRectP9CGContextPK14__CFDictionaryPS5_
 }
 {
+   bug_173779_b
+   Memcheck:Uninitialized
+   ...
+   fun:img_data_lock
+   fun:CGSImageDataLock
+   fun:ripc_AcquireImage
+   fun:ripc_DrawImage*
+   fun:CGContextDrawImage*
+   ...
+   fun:-[NSImage hitTestRect:withImageDestinationRect:context:hints:flipped:]
+}
+{
   bug_340726
   Memcheck:Leak
   fun:_Znw*
   fun:_ZN4base17LoadNativeLibrary*
   fun:_ZN3gfx26InitializeStaticGLBindings*
   fun:_ZN3gfx9GLSurface30InitializeOneOffImplementation*
   fun:_ZN3gfx9GLSurface24InitializeOneOffForTestsEv
 }
 {
    bug_380568
@@ skipping 30 matching lines @@
    fun:_ZN7content45PluginLoaderPosixTest_PluginLaunchFailed_TestC1Ev
    fun:_ZN7testing8internal15TestFactoryImplIN7content45PluginLoaderPosixTest_PluginLaunchFailed_TestEE10CreateTestEv
 }
 {
    bug_437807
    Memcheck:Leak
    ...
    fun:_ZN4base3mac30PathForFrameworkBundleResourceEPK10__CFString
    fun:_ZN3gin13IsolateHolder14LoadV8SnapshotEv
 }