SkScalerContextRec::computeMatrices to return status.

When computing the matricies for a scaler context, there is a special
case when the matrix is determined to be singular. No port properly
handles zero sized text, so we detect this case and return a 'normal'
text size and a zero matrix for all computed transformations. This
CL causes computeMatricies to return 'false' in this case.

This is used in the constructor of SkScalerContext_Mac in order to
avoid calling CGAffineTransformInvert on non-invertible transformations.
CGAffineTransformInvert documents that if the transform is
non-invertible it will return the passed transform unchanged. It does
so, but then also prints a message to stdout. Since the information is
already available to avoid this chatty behavior, use it to keep things
quiet.

BUG=skia:3231,chromium:630169
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2276583003

Review-Url: https://codereview.chromium.org/2276583003
diff --git a/src/core/SkScalerContext.cpp b/src/core/SkScalerContext.cpp
index 85e8994..ecac82a 100644
--- a/src/core/SkScalerContext.cpp
+++ b/src/core/SkScalerContext.cpp
@@ -687,7 +687,7 @@
     m->postConcat(deviceMatrix);
 }
 
-void SkScalerContextRec::computeMatrices(PreMatrixScale preMatrixScale, SkVector* s, SkMatrix* sA,
+bool SkScalerContextRec::computeMatrices(PreMatrixScale preMatrixScale, SkVector* s, SkMatrix* sA,
                                          SkMatrix* GsA, SkMatrix* G_inv, SkMatrix* A_out)
 {
     // A is the 'total' matrix.
@@ -723,7 +723,7 @@
         if (G_inv) {
             G_inv->reset();
         }
-        return;
+        return false;
     }
 
     // GA is the matrix A with rotation removed.
@@ -803,6 +803,8 @@
          // G is rotational so reorders with the scale.
         GsA->preScale(SkScalarInvert(s->fX), SkScalarInvert(s->fY));
     }
+
+    return true;
 }
 
 SkAxisAlignment SkScalerContext::computeAxisAlignmentForHText() {