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

gm/SkAnimTimer.h

Index: gm/SkAnimTimer.h
diff --git a/gm/SkAnimTimer.h b/gm/SkAnimTimer.h
index 725171a8fe55034ab223565f8653016571cf22c2..2c8a723e5bb970d0799e1a802536ad5e6715b95a 100644
--- a/gm/SkAnimTimer.h
+++ b/gm/SkAnimTimer.h
@@ -29,7 +29,7 @@ public:
     /**
      *  Class begins in the "stopped" state.
      */
-    SkAnimTimer() : fBaseTime(0), fCurrTime(0), fState(kStopped_State) {}
+    SkAnimTimer() : fBaseTimeNanos(0), fCurrTimeNanos(0), fState(kStopped_State) {}
 
     bool isStopped() const { return kStopped_State == fState; }
     bool isRunning() const { return kRunning_State == fState; }
@@ -70,23 +70,26 @@ public:
      */
     void updateTime() {
         if (kRunning_State == fState) {
-            fCurrTime = SkTime::GetMSecs();
+            fCurrTimeNanos = SkTime::GetNSecs();
         }
     }
 
     /**
      *  Return the time in milliseconds the timer has been in the running state.
-     *  Returns 0 if the timer is stopped.
+     *  Returns 0 if the timer is stopped. Behavior is undefined if the timer
+     *  has been running longer than SK_MSecMax.
      */
-    SkMSec msec() const { return fCurrTime - fBaseTime; }
+    SkMSec msec() const {
+        const double msec = (fCurrTimeNanos - fBaseTimeNanos) * 1e-6;
+        SkASSERT(SK_MSecMax >= msec);
+        return static_cast<SkMSec>(msec);
+    }
 
     /**
      *  Return the time in seconds the timer has been in the running state.
      *  Returns 0 if the timer is stopped.
      */
-    double secs() const {
-        return this->msec() * 0.001;
-    }
+    double secs() const { return (fCurrTimeNanos - fBaseTimeNanos) * 1e-9; }
 
     /**
      *  Return the time in seconds the timer has been in the running state,
@@ -102,14 +105,14 @@ public:
     }
 
 private:
-    SkMSec  fBaseTime;
-    SkMSec  fCurrTime;
+    double  fBaseTimeNanos;
+    double  fCurrTimeNanos;
     State   fState;
 
     void setState(State newState) {
         switch (newState) {
             case kStopped_State:
-                fBaseTime = fCurrTime = 0;
+                fBaseTimeNanos = fCurrTimeNanos = 0;
                 fState = kStopped_State;
                 break;
             case kPaused_State:
@@ -120,12 +123,12 @@ private:
             case kRunning_State:
                 switch (fState) {
                     case kStopped_State:
-                        fBaseTime = fCurrTime = SkTime::GetMSecs();
+                        fBaseTimeNanos = fCurrTimeNanos = SkTime::GetNSecs();
                         break;
                     case kPaused_State: {// they want "resume"
-                        SkMSec now = SkTime::GetMSecs();
-                        fBaseTime += now - fCurrTime;
-                        fCurrTime = now;
+                        double now = SkTime::GetNSecs();
+                        fBaseTimeNanos += now - fCurrTimeNanos;
+                        fCurrTimeNanos = now;
                     } break;
                     case kRunning_State:
                         break;