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/PathTest.cpp b/tests/PathTest.cpp
index a52e540..d8da95b 100644
--- a/tests/PathTest.cpp
+++ b/tests/PathTest.cpp
@@ -290,7 +290,7 @@
 // Note: PathBench::ArbRoundRectBench performs almost exactly
 // the same test (but with drawing)
 static void test_arb_round_rect_is_convex(skiatest::Reporter* reporter) {
-    SkRandom rand;
+    SkMWCRandom rand;
     SkRect r;
 
     for (int i = 0; i < 5000; ++i) {
@@ -317,7 +317,7 @@
 // Note: PathBench::ArbRoundRectBench performs almost exactly
 // the same test (but with drawing)
 static void test_arb_zero_rad_round_rect_is_rect(skiatest::Reporter* reporter) {
-    SkRandom rand;
+    SkMWCRandom rand;
     SkRect r;
 
     for (int i = 0; i < 5000; ++i) {
@@ -452,7 +452,7 @@
 
 static void test_addPoly(skiatest::Reporter* reporter) {
     SkPoint pts[32];
-    SkRandom rand;
+    SkMWCRandom rand;
 
     for (size_t i = 0; i < SK_ARRAY_COUNT(pts); ++i) {
         pts[i].fX = rand.nextSScalar1();
@@ -1862,7 +1862,7 @@
     }
 
     // Max of 10 segments, max 3 points per segment
-    SkRandom rand(9876543);
+    SkMWCRandom rand(9876543);
     SkPoint          expectedPts[31]; // May have leading moveTo
     SkPath::Verb     expectedVerbs[22]; // May have leading moveTo
     SkPath::Verb     nextVerb;