doc: Make Doxygen-generated HTML interface documentation prettier

This provides custom CSS to override Doxygen’s default font choices.
It uses the Open Sans and Source Code Pro as used on Gitiles and
PolyGerrit.

A slightly-improved Doxygen main page is included as well.

Change-Id: Ib9f7e7d3eef7d3b78231e2dc9430aa8758590773
Reviewed-on: https://chromium-review.googlesource.com/408715
Reviewed-by: Robert Sesek <rsesek@chromium.org>

doc/support/crashpad.doxy

@@ -1129,7 +1129,7 @@ HTML_STYLESHEET        =
 # list). For an example see the documentation.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
-HTML_EXTRA_STYLESHEET  =
+HTML_EXTRA_STYLESHEET  = doc/support/crashpad_doxygen.css
 
 # The HTML_EXTRA_FILES tag can be used to specify one or more extra images or
 # other source files which should be copied to the HTML output directory. Note

doc/support/crashpad.doxy.h

@@ -22,3 +22,13 @@
 
 //! \namespace crashpad::test
 //! \brief The testing namespace, for use in test code only.
+
+//! \mainpage Crashpad Interface Documentation
+//!
+//! Most generated interface documentation is reachable through <a
+//! href="namespaces.html">Namespaces</a>, <a href="annotated.html">Classes</a>
+//! (includes `struct`s, `union`s, and interfaces), or <a
+//! href="files.html">Files</a> (includes macros).
+//!
+//! Additional documentation is available at the <a
+//! href="https://crashpad.chromium.org/">Crashpad home page</a>.

doc/support/crashpad_doxygen.css

@@ -0,0 +1,60 @@
+/* Copyright 2016 The Crashpad Authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License. */
+
+@import "https://fonts.googleapis.com/css?family=Open+Sans:300,400,700&subset=latin,cyrillic-ext,greek-ext,cyrillic,greek,vietnamese,latin-ext";
+@import "https://fonts.googleapis.com/css?family=Source+Code+Pro";
+
+body,
+table,
+div,
+p,
+dl,
+.title,
+.icon,
+table.directory,
+.navpath li.navelem a,
+#projectname,
+#projectbrief,
+#projectnumber,
+div.toc li,
+div.toc h3,
+#powerTip div,
+.sm-dox a,
+.sm-dox a:focus,
+.sm-dox a:hover,
+.sm-dox a:active {
+  font-family: 'Open Sans',
+               'Lucida Grande',
+               'Lucida Sans Unicode',
+               Helvetica,
+               Arial,
+               sans-serif;
+}
+
+code,
+tt,
+pre.fragment,
+div.line,
+.overload,
+.params .paramdir,
+.sm-dox a span.sub-arrow {
+  font-family: 'Source Code Pro',
+               Monaco,
+               'Lucida Console',
+               monospace;
+}
+
+.icon {
+  height: auto;
+}