speed up debug dm

SkPathMeasure can take minutes with pathological cases.
Limit the debug check to a reasonable number.

R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2356343004

Review-Url: https://codereview.chromium.org/2356343004
diff --git a/src/core/SkPathMeasure.cpp b/src/core/SkPathMeasure.cpp
index b802674..8582bc2 100644
--- a/src/core/SkPathMeasure.cpp
+++ b/src/core/SkPathMeasure.cpp
@@ -407,14 +407,15 @@
         const Segment* stop = fSegments.end();
         unsigned        ptIndex = 0;
         SkScalar        distance = 0;
-
+        // limit the loop to a reasonable number; pathological cases can run for minutes
+        int             maxChecks = 10000000;  // set to INT_MAX to defeat the check
         while (seg < stop) {
             SkASSERT(seg->fDistance > distance);
             SkASSERT(seg->fPtIndex >= ptIndex);
             SkASSERT(seg->fTValue > 0);
 
             const Segment* s = seg;
-            while (s < stop - 1 && s[0].fPtIndex == s[1].fPtIndex) {
+            while (s < stop - 1 && s[0].fPtIndex == s[1].fPtIndex && --maxChecks > 0) {
                 SkASSERT(s[0].fType == s[1].fType);
                 SkASSERT(s[0].fTValue < s[1].fTValue);
                 s += 1;