Change random number generator for 'tests' to SkMWCRandom. Also removes some 
unused headers and fixes a couple of bugs exposed by changing the random 
number generator:

First, the function SkMatrix::getMaxStretch() had an error where it was testing
the square of a number against near-zero. This led to it occasionally taking a
cheaper but imprecise path for computing the eigenvalues of the matrix. It's 
been replaced with a check against the square of SK_ScalarNearlyZero. 

The second case was a failure in ClipStackTest, where it hit the rare case of 
a practically empty clip stack (it has a single Union) and we set a tight 
bounds. The bounds rect doesn't get set by GrReducedClip::ReduceClipStack() in 
this case, so when it clips the reduced stack it's clipping against garbage, 
and the resulting regions don't match. The solution is to initialize the 
tightBounds rect.


git-svn-id: http://skia.googlecode.com/svn/trunk@7952 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tests/SortTest.cpp b/tests/SortTest.cpp
index 28c6e68..6bfb300 100644
--- a/tests/SortTest.cpp
+++ b/tests/SortTest.cpp
@@ -15,7 +15,7 @@
     }
 }
 
-static void rand_array(SkRandom& rand, int array[], int n) {
+static void rand_array(SkMWCRandom& rand, int array[], int n) {
     for (int j = 0; j < n; j++) {
         array[j] = rand.nextS() & 0xFF;
     }
@@ -40,7 +40,7 @@
     /** The random numbers are copied into this array, sorted by an SkSort,
         then this array is compared against the reference sort. */
     int workingArray[SK_ARRAY_COUNT(randomArray)];
-    SkRandom    rand;
+    SkMWCRandom    rand;
 
     for (int i = 0; i < 10000; i++) {
         int count = rand.nextRangeU(1, SK_ARRAY_COUNT(randomArray));