Limit backing scale factor to 100X

Previous to this CL, any value could be passed to this function,
which caused problems if very large values were used. See
https://crbug.com/899482 for an example. Per the discussion there,
100X seems like a reasonable limit.

Bug: 899482
Change-Id: I0ed9b68510bf9462c76dcf85e6954df416c0df2f
Reviewed-on: https://chromium-review.googlesource.com/c/1320015Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Mike Pinkerton <pinkerton@chromium.org>
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606067}

content/shell/test_runner/test_runner.cc

@@ -1244,8 +1244,12 @@ std::string TestRunnerBindings::PathToLocalResource(const std::string& path) {
 void TestRunnerBindings::SetBackingScaleFactor(
     double value,
     v8::Local<v8::Function> callback) {
+  // Limit backing scale factor to something "reasonable" - 100x. Without
+  // this limit, arbitrarily large values can be used, which can lead to
+  // crashes and other problems: See https://crbug.com/899482.
+  double limited_value = fmin(100.0, value);
   if (view_runner_)
-    view_runner_->SetBackingScaleFactor(value, callback);
+    view_runner_->SetBackingScaleFactor(limited_value, callback);
 }
 
 void TestRunnerBindings::EnableUseZoomForDSF(v8::Local<v8::Function> callback) {