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/src/gpu/GrRedBlackTree.h b/src/gpu/GrRedBlackTree.h
index 2ccf77f..ba03be2 100644
--- a/src/gpu/GrRedBlackTree.h
+++ b/src/gpu/GrRedBlackTree.h
@@ -950,7 +950,7 @@
     GrRedBlackTree<int> tree;
     typedef GrRedBlackTree<int>::Iter iter;
 
-    SkRandom r;
+    SkMWCRandom r;
 
     int count[100] = {0};
     // add 10K ints