Change SkTime::GetMSecs to double; ensure values stored in SkMSec do not overflow.

src/images/SkImageDecoder_libwebp.cpp

Index: src/images/SkImageDecoder_libwebp.cpp
diff --git a/src/images/SkImageDecoder_libwebp.cpp b/src/images/SkImageDecoder_libwebp.cpp
index 2db08cee83dd5fd3ceb054a2e515ae12af8cd2cf..e3951f8fc706d90bedca2194962a00de313e16d1 100644
--- a/src/images/SkImageDecoder_libwebp.cpp
+++ b/src/images/SkImageDecoder_libwebp.cpp
@@ -131,23 +131,6 @@ private:
 
 #include "SkTime.h"
 
-class AutoTimeMillis {
-public:
-    AutoTimeMillis(const char label[]) :
-        fLabel(label) {
-        if (nullptr == fLabel) {
-            fLabel = "";
-        }
-        fNow = SkTime::GetMSecs();
-    }
-    ~AutoTimeMillis() {
-        SkDebugf("---- Time (ms): %s %d\n", fLabel, SkTime::GetMSecs() - fNow);
-    }
-private:
-    const char* fLabel;
-    SkMSec fNow;
-};
-
 #endif
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -286,7 +269,7 @@ bool SkWEBPImageDecoder::setDecodeConfig(SkBitmap* decodedBitmap, int width, int
 SkImageDecoder::Result SkWEBPImageDecoder::onDecode(SkStream* stream, SkBitmap* decodedBitmap,
                                                     Mode mode) {
 #ifdef TIME_DECODE
-    AutoTimeMillis atm("WEBP Decode");
+    SkAutoTime atm("WEBP Decode");
 #endif
 
     int origWidth, origHeight, hasAlpha;