cc: Do not create separate tilings for almost equal scale factors.

cc/base/math_util.h

Index: cc/base/math_util.h
diff --git a/cc/base/math_util.h b/cc/base/math_util.h
index a83ab4fdce34be03b56fd23ffe978262abbe69fb..3a688d1ea95bae232ae3c9e1dfc383fb149c3a88 100644
--- a/cc/base/math_util.h
+++ b/cc/base/math_util.h
@@ -97,6 +97,20 @@ class CC_EXPORT MathUtil {
     return (d > 0.0) ? std::floor(d + 0.5) : std::ceil(d - 0.5);
   }
 
+  // Rounds the given |value| to fixed precision. This makes almost equal
+  // floats (which differ by some threshold magnitude of floating point epsilon)
+  // to be considered as same.
+  // The |precision| should be >= 0, otherwise crashes in debug builds.
+  // The max number of digits that can be represented without change by float
+  // is 6. The maximum possible digits in the fraction part is computed by
+  // considering digits in integral part and digits required for |precision|.
+  // e.g. If intergral part has 4 digits and precision in fractional part
+  // requested is 5, then max allowed precision for fraction part is 2.
+  // Examples:
+  // RoundToFixedPrecision(7.33907556533813, 4) returns 7.339000225067138671875.
+  // RoundToFixedPrecision(7.33907508850098, 4) returns 7.339000225067138671875.
+  static float RoundToFixedPrecision(float value, int precision);
+
   // Returns true if rounded up value does not overflow, false otherwise.
   template <typename T>
   static bool VerifyRoundup(T n, T mul) {