Add PRESUBMIT check to cc to ensure that C++ std::abs is used

This is try #2, previous patch r214144 was reverted in r214149.

Before this patch, it is possible to use abs() without the std::
namespace qualifier, which may link to the C standard library
implementation of abs(). Thus, someone using abs(float) may get
wrong results because C standard version will convert the float
to an int. This patch updates the occurrences of of abs() and
fabs() in cc/ (though technically none were incorrect, thankfully)
and adds a PRESUBMIT to enforce that all uses of abs from now on
have an explicit std:: to resolve them correctly.

BUG=261900
R=enne@chromium.org

Review URL: https://codereview.chromium.org/21061004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@214225 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 4 insertions, 3 deletions

diff --git a/cc/animation/timing_function.cc b/cc/animation/timing_function.cc
index f5a4f9f..65d607f 100644
--- a/cc/animation/timing_function.cc
+++ b/cc/animation/timing_function.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include <algorithm>
+#include <cmath>
 
 #include "base/logging.h"
 #include "cc/animation/timing_function.h"
@@ -47,14 +48,14 @@ static double bezier_interp(double x1,
   double step = 1.0;
   for (int i = 0; i < MAX_STEPS; ++i, step *= 0.5) {
     const double error = eval_bezier(x1, x2, t) - x;
-    if (fabs(error) < BEZIER_EPSILON)
+    if (std::abs(error) < BEZIER_EPSILON)
       break;
     t += error > 0.0 ? -step : step;
   }
 
   // We should have terminated the above loop because we got close to x, not
   // because we exceeded MAX_STEPS. Do a DCHECK here to confirm.
-  DCHECK_GT(BEZIER_EPSILON, fabs(eval_bezier(x1, x2, t) - x));
+  DCHECK_GT(BEZIER_EPSILON, std::abs(eval_bezier(x1, x2, t) - x));
 
   // Step 2. Return the interpolated y values at the t we computed above.
   return eval_bezier(y1, y2, t);
diff --git a/cc/animation/transform_operation.cc b/cc/animation/transform_operation.cc
index 854901d..dacea06 100644
--- a/cc/animation/transform_operation.cc
+++ b/cc/animation/transform_operation.cc
@@ -60,7 +60,7 @@ static bool ShareSameAxis(const TransformOperation* from,
   double dot = to->rotate.axis.x * from->rotate.axis.x +
                to->rotate.axis.y * from->rotate.axis.y +
                to->rotate.axis.z * from->rotate.axis.z;
-  double error = std::fabs(1.0 - (dot * dot) / (length_2 * other_length_2));
+  double error = std::abs(1.0 - (dot * dot) / (length_2 * other_length_2));
   bool result = error < kAngleEpsilon;
   if (result) {
     *axis_x = to->rotate.axis.x;