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/ClipStackTest.cpp b/tests/ClipStackTest.cpp
index 4709d22..4de6673 100644
--- a/tests/ClipStackTest.cpp
+++ b/tests/ClipStackTest.cpp
@@ -820,7 +820,7 @@
         add_oval,
     };
 
-    SkRandom r;
+    SkMWCRandom r;
 
     for (int i = 0; i < kNumTests; ++i) {
         // Randomly generate a clip stack.
@@ -864,7 +864,7 @@
         ElementList reducedClips;
 
         GrReducedClip::InitialState initial;
-        SkIRect tBounds;
+        SkIRect tBounds(inflatedIBounds);
         SkIRect* tightBounds = r.nextBool() ? &tBounds : NULL;
         GrReducedClip::ReduceClipStack(stack,
                                        inflatedIBounds,