Fix valgrind warnings in YUV scaling code.

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 # running overnight and removing outdated bugs/suppressions.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 1992 matching lines @@
    fun:_ZN3gfx46VideoDecodeAccelerationSupportTest_Create_Test8TestBodyEv
 }
 {
    bug_131361
    Memcheck:Overlap
    fun:memcpy
    ...
    fun:_ZN2v88internal18GvnBasicBlockState32*
 }
 {
-   bug_139633
-   Memcheck:Uninitialized
-   fun:_ZL19ConvertYUVToRGB32_ChhhPh
-   fun:LinearScaleYUVToRGB32RowWithRange_C
-   fun:_ZN5media23ScaleYUVToRGB32WithRectEPKhS1_S1_Phiiiiiiiiiii
-   fun:_ZN8remoting29ConvertAndScaleYUVToRGB32RectEPKhS1_S1_iiRK7SkTSizeIiERK7SkIRectPhiS5_S8_S8_
-   fun:_ZN8remoting10DecoderVp811RenderFrameERK7SkTSizeIiERK7SkIRectPhiP8SkRegion
-   fun:_ZN8remoting13DecoderTester11RenderFrameEv
-   fun:_ZN8remoting13DecoderTester14ReceivedPacketEPNS_11VideoPacketE
-   fun:_ZN8remoting13DecoderTester20ReceivedScopedPacketE10scoped_ptrINS_11VideoPacketEE
-}
-{
    bug_148865
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN7content16RenderThreadImpl4InitEv
    fun:_ZN7content16RenderThreadImplC2ERKSs
    fun:_ZN7content16RenderThreadImplC1ERKSs
    fun:_ZN7content21WebRTCAudioDeviceTest5SetUpEv
 }
 {
    bug_159190
@@ skipping 356 matching lines @@
    fun:_Znw*
    fun:_ZN7WebCore7RuleSet18ensurePendingRulesEv
    fun:_ZN7WebCore7RuleSet21findBestRuleSetAndAdd*
    fun:_ZN7WebCore7RuleSet7addRule*
    fun:_ZN7WebCore7RuleSet13addChildRules*
    fun:_ZN7WebCore7RuleSet17addRulesFromSheet*
    fun:_ZN7WebCore21CSSDefaultStyleSheets16loadDefaultStyleEv
    fun:_ZN7WebCore21CSSDefaultStyleSheets32loadDefaultStylesheetIfNecessaryEv
    fun:_ZN7WebCore13StyleResolver*
 }